diff --git a/src/detect-antipatterns-browser.js b/src/detect-antipatterns-browser.js
index e181ccb08..3162f43e7 100644
--- a/src/detect-antipatterns-browser.js
+++ b/src/detect-antipatterns-browser.js
@@ -48,6 +48,18 @@ const SAFE_TAGS = new Set([
   'rect', 'line', 'polyline', 'polygon', 'g', 'defs', 'use',
 ]);
 
+// Per-check safe-tags override for the border (side-tab / border-accent)
+// rule. We intentionally re-allow <label> here because card-shaped clickable
+// labels (e.g. .checklist-item wrapping a checkbox + content) are one of the
+// canonical side-tab anti-pattern shapes and must be detected. The rule's
+// other preconditions (non-neutral color, width >= 2px on a single side,
+// radius > 0 or width >= 3, element size >= 20x20 in the browser path)
+// already filter out plain inline form labels so this does not introduce
+// false positives. See modern-color-borders.html for the test matrix.
+const BORDER_SAFE_TAGS = new Set(
+  [...SAFE_TAGS].filter(t => t !== 'label')
+);
+
 const OVERUSED_FONTS = new Set([
   'inter', 'roboto', 'open sans', 'lato', 'montserrat', 'arial', 'helvetica',
 ]);
@@ -300,9 +312,53 @@ const ANTIPATTERNS = [
 
 function isNeutralColor(color) {
   if (!color || color === 'transparent') return true;
-  const m = color.match(/rgba?\((\d+),\s*(\d+),\s*(\d+)/);
-  if (!m) return true;
-  return (Math.max(+m[1], +m[2], +m[3]) - Math.min(+m[1], +m[2], +m[3])) < 30;
+
+  // rgb/rgba — use channel spread. Threshold 30 ≈ 11.7% of the 0–255 range.
+  const rgb = color.match(/rgba?\((\d+),\s*(\d+),\s*(\d+)/);
+  if (rgb) {
+    return (Math.max(+rgb[1], +rgb[2], +rgb[3]) - Math.min(+rgb[1], +rgb[2], +rgb[3])) < 30;
+  }
+
+  // oklch()/lch() — chroma is the second numeric component.
+  // oklch chroma is ~0–0.4 in sRGB gamut; >= 0.02 reads as tinted, not gray.
+  // lch chroma is ~0–150; >= 3 reads as tinted. jsdom emits both formats
+  // literally (it does NOT convert them to rgb).
+  const oklch = color.match(/oklch\(\s*[\d.%-]+\s+([\d.-]+)/i);
+  if (oklch) return parseFloat(oklch[1]) < 0.02;
+  const lch = color.match(/lch\(\s*[\d.%-]+\s+([\d.-]+)/i);
+  if (lch) return parseFloat(lch[1]) < 3;
+
+  // oklab()/lab() — a and b are signed axes; chroma = sqrt(a² + b²).
+  // oklab a/b are ~-0.4..0.4, threshold 0.02. lab a/b are ~-128..127, threshold 3.
+  const oklab = color.match(/oklab\(\s*[\d.%-]+\s+([\d.-]+)\s+([\d.-]+)/i);
+  if (oklab) {
+    const a = parseFloat(oklab[1]), b = parseFloat(oklab[2]);
+    return Math.hypot(a, b) < 0.02;
+  }
+  const lab = color.match(/lab\(\s*[\d.%-]+\s+([\d.-]+)\s+([\d.-]+)/i);
+  if (lab) {
+    const a = parseFloat(lab[1]), b = parseFloat(lab[2]);
+    return Math.hypot(a, b) < 3;
+  }
+
+  // hsl/hsla — saturation is the second numeric component (percent).
+  // Modern jsdom usually converts hsl() to rgb, but handle it directly for
+  // safety across versions and for any engine that preserves the format.
+  const hsl = color.match(/hsla?\(\s*[\d.-]+\s*,?\s*([\d.]+)%/i);
+  if (hsl) return parseFloat(hsl[1]) < 10;
+
+  // hwb(hue whiteness% blackness%) — a pixel is fully gray when
+  // whiteness + blackness >= 100; chroma-like saturation = 1 - (w+b)/100.
+  const hwb = color.match(/hwb\(\s*[\d.-]+\s+([\d.]+)%\s+([\d.]+)%/i);
+  if (hwb) {
+    const w = parseFloat(hwb[1]), b = parseFloat(hwb[2]);
+    return (1 - Math.min(100, w + b) / 100) < 0.1;
+  }
+
+  // Unknown / unrecognized format — err on the side of DETECTING rather
+  // than silently skipping. This is the opposite of the previous default,
+  // which was the root cause of the oklch bug.
+  return false;
 }
 
 function parseRgb(color) {
@@ -369,7 +425,7 @@ function colorToHex(c) {
 // ─── Section 3: Pure Detection ──────────────────────────────────────────────
 
 function checkBorders(tag, widths, colors, radius) {
-  if (SAFE_TAGS.has(tag)) return [];
+  if (BORDER_SAFE_TAGS.has(tag)) return [];
   const findings = [];
   const sides = ['Top', 'Right', 'Bottom', 'Left'];
 
@@ -833,7 +889,7 @@ function resolveGradientStops(el, win) {
 
 function checkElementBordersDOM(el) {
   const tag = el.tagName.toLowerCase();
-  if (SAFE_TAGS.has(tag)) return [];
+  if (BORDER_SAFE_TAGS.has(tag)) return [];
   const rect = el.getBoundingClientRect();
   if (rect.width < 20 || rect.height < 20) return [];
   const style = getComputedStyle(el);
diff --git a/src/detect-antipatterns.mjs b/src/detect-antipatterns.mjs
index 6dad21522..4f4bf2ad3 100644
--- a/src/detect-antipatterns.mjs
+++ b/src/detect-antipatterns.mjs
@@ -43,6 +43,18 @@ const SAFE_TAGS = new Set([
   'rect', 'line', 'polyline', 'polygon', 'g', 'defs', 'use',
 ]);
 
+// Per-check safe-tags override for the border (side-tab / border-accent)
+// rule. We intentionally re-allow <label> here because card-shaped clickable
+// labels (e.g. .checklist-item wrapping a checkbox + content) are one of the
+// canonical side-tab anti-pattern shapes and must be detected. The rule's
+// other preconditions (non-neutral color, width >= 2px on a single side,
+// radius > 0 or width >= 3, element size >= 20x20 in the browser path)
+// already filter out plain inline form labels so this does not introduce
+// false positives. See modern-color-borders.html for the test matrix.
+const BORDER_SAFE_TAGS = new Set(
+  [...SAFE_TAGS].filter(t => t !== 'label')
+);
+
 const OVERUSED_FONTS = new Set([
   'inter', 'roboto', 'open sans', 'lato', 'montserrat', 'arial', 'helvetica',
 ]);
@@ -295,9 +307,53 @@ const ANTIPATTERNS = [
 
 function isNeutralColor(color) {
   if (!color || color === 'transparent') return true;
-  const m = color.match(/rgba?\((\d+),\s*(\d+),\s*(\d+)/);
-  if (!m) return true;
-  return (Math.max(+m[1], +m[2], +m[3]) - Math.min(+m[1], +m[2], +m[3])) < 30;
+
+  // rgb/rgba — use channel spread. Threshold 30 ≈ 11.7% of the 0–255 range.
+  const rgb = color.match(/rgba?\((\d+),\s*(\d+),\s*(\d+)/);
+  if (rgb) {
+    return (Math.max(+rgb[1], +rgb[2], +rgb[3]) - Math.min(+rgb[1], +rgb[2], +rgb[3])) < 30;
+  }
+
+  // oklch()/lch() — chroma is the second numeric component.
+  // oklch chroma is ~0–0.4 in sRGB gamut; >= 0.02 reads as tinted, not gray.
+  // lch chroma is ~0–150; >= 3 reads as tinted. jsdom emits both formats
+  // literally (it does NOT convert them to rgb).
+  const oklch = color.match(/oklch\(\s*[\d.%-]+\s+([\d.-]+)/i);
+  if (oklch) return parseFloat(oklch[1]) < 0.02;
+  const lch = color.match(/lch\(\s*[\d.%-]+\s+([\d.-]+)/i);
+  if (lch) return parseFloat(lch[1]) < 3;
+
+  // oklab()/lab() — a and b are signed axes; chroma = sqrt(a² + b²).
+  // oklab a/b are ~-0.4..0.4, threshold 0.02. lab a/b are ~-128..127, threshold 3.
+  const oklab = color.match(/oklab\(\s*[\d.%-]+\s+([\d.-]+)\s+([\d.-]+)/i);
+  if (oklab) {
+    const a = parseFloat(oklab[1]), b = parseFloat(oklab[2]);
+    return Math.hypot(a, b) < 0.02;
+  }
+  const lab = color.match(/lab\(\s*[\d.%-]+\s+([\d.-]+)\s+([\d.-]+)/i);
+  if (lab) {
+    const a = parseFloat(lab[1]), b = parseFloat(lab[2]);
+    return Math.hypot(a, b) < 3;
+  }
+
+  // hsl/hsla — saturation is the second numeric component (percent).
+  // Modern jsdom usually converts hsl() to rgb, but handle it directly for
+  // safety across versions and for any engine that preserves the format.
+  const hsl = color.match(/hsla?\(\s*[\d.-]+\s*,?\s*([\d.]+)%/i);
+  if (hsl) return parseFloat(hsl[1]) < 10;
+
+  // hwb(hue whiteness% blackness%) — a pixel is fully gray when
+  // whiteness + blackness >= 100; chroma-like saturation = 1 - (w+b)/100.
+  const hwb = color.match(/hwb\(\s*[\d.-]+\s+([\d.]+)%\s+([\d.]+)%/i);
+  if (hwb) {
+    const w = parseFloat(hwb[1]), b = parseFloat(hwb[2]);
+    return (1 - Math.min(100, w + b) / 100) < 0.1;
+  }
+
+  // Unknown / unrecognized format — err on the side of DETECTING rather
+  // than silently skipping. This is the opposite of the previous default,
+  // which was the root cause of the oklch bug.
+  return false;
 }
 
 function parseRgb(color) {
@@ -364,7 +420,7 @@ function colorToHex(c) {
 // ─── Section 3: Pure Detection ──────────────────────────────────────────────
 
 function checkBorders(tag, widths, colors, radius) {
-  if (SAFE_TAGS.has(tag)) return [];
+  if (BORDER_SAFE_TAGS.has(tag)) return [];
   const findings = [];
   const sides = ['Top', 'Right', 'Bottom', 'Left'];
 
@@ -828,7 +884,7 @@ function resolveGradientStops(el, win) {
 
 function checkElementBordersDOM(el) {
   const tag = el.tagName.toLowerCase();
-  if (SAFE_TAGS.has(tag)) return [];
+  if (BORDER_SAFE_TAGS.has(tag)) return [];
   const rect = el.getBoundingClientRect();
   if (rect.width < 20 || rect.height < 20) return [];
   const style = getComputedStyle(el);
diff --git a/tests/detect-antipatterns-fixtures.test.mjs b/tests/detect-antipatterns-fixtures.test.mjs
index 582315566..01308f6fe 100644
--- a/tests/detect-antipatterns-fixtures.test.mjs
+++ b/tests/detect-antipatterns-fixtures.test.mjs
@@ -82,6 +82,43 @@ describe('detectHtml — jsdom fixtures', () => {
     assert.ok(borderFindings.length <= 1);
   });
 
+  it('modern-color-borders: oklch/oklab/lch/lab side-tabs are flagged, neutrals pass', async () => {
+    // Regression for the isNeutralColor bug where any non-rgb() color format
+    // (oklch, oklab, lch, lab — which jsdom does NOT normalize to rgb) was
+    // misclassified as neutral, causing checkBorders() to silently skip
+    // every element with a modern-color side border.
+    //
+    // Also regression for the SAFE_TAGS/label bug: card-shaped <label>
+    // elements (clickable checklist rows with padding + radius + colored
+    // side border) used to be silently skipped because checkBorders'
+    // SAFE_TAGS gate excluded <label>. The fix narrows that gate so card-
+    // shaped labels are checked while plain inline form labels still pass.
+    const f = await detectHtml(path.join(FIXTURES, 'modern-color-borders.html'));
+    const sideTabs = f.filter(r => r.antipattern === 'side-tab');
+    // Eight FLAG cases: oklch x3, oklab, lch, lab — all colored border-left
+    // with a non-zero border-radius — plus two card-shaped <label> cases
+    // (one oklch, one rgb). Each must produce exactly one side-tab.
+    assert.equal(
+      sideTabs.length, 8,
+      `expected 8 side-tab findings from the FLAG column, got ${sideTabs.length}: ${sideTabs.map(r => r.snippet).join('; ')}`
+    );
+    // Every finding must be a border-left (never right/top/bottom) since
+    // that's the only side the fixture decorates.
+    for (const r of sideTabs) {
+      assert.match(r.snippet || '', /border-left:/, `expected border-left, got ${r.snippet}`);
+    }
+    // PASS column must contribute zero border findings of either flavor.
+    // There are 10 pass cases: 6 structural neutrals plus 4 labels (plain
+    // inline form label, label with a neutral gray border, label in a form
+    // row, and a label with a thin 1px colored left border). If any leaks
+    // through, the label exception is over-broad.
+    const borderAccent = f.filter(r => r.antipattern === 'border-accent-on-rounded');
+    assert.equal(
+      borderAccent.length, 0,
+      `expected 0 border-accent-on-rounded, got ${borderAccent.length}: ${borderAccent.map(r => r.snippet).join('; ')}`
+    );
+  });
+
   it('typography-should-flag: detects all three issues', async () => {
     const f = await detectHtml(path.join(FIXTURES, 'typography-should-flag.html'));
     assert.ok(f.some(r => r.antipattern === 'overused-font'));
diff --git a/tests/fixtures/antipatterns/modern-color-borders.html b/tests/fixtures/antipatterns/modern-color-borders.html
new file mode 100644
index 000000000..5fd840f8d
--- /dev/null
+++ b/tests/fixtures/antipatterns/modern-color-borders.html
@@ -0,0 +1,235 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <title>Side-Tab with Modern Color Formats (oklch/lab/lch/hsl/hwb)</title>
+  <style>
+    /* Two-column fixture: left col = should-flag, right col = should-pass.
+       The side-tab snippet doesn't embed identifying text, so the test
+       asserts finding counts against the structural ids (#flag-N / #pass-N)
+       by reading the element via data attributes in the check path. Since
+       that isn't available to the Node fixture runner, we instead place a
+       unique number of FLAG elements (each a distinct side-tab) and verify
+       the side-tab count. */
+
+    body { font-family: system-ui, sans-serif; margin: 0; padding: 24px; background: #fafafa; }
+    .grid { display: grid; grid-template-columns: 1fr 1fr; gap: 32px; max-width: 1120px; margin: 0 auto; }
+    .col h2 { font-size: 14px; text-transform: uppercase; letter-spacing: 0.05em; margin: 0 0 16px; color: #475569; }
+    .case { padding: 12px 16px; margin-bottom: 16px; }
+    .case h3 { font-size: 14px; margin: 0 0 4px; }
+    .case p { font-size: 13px; margin: 0; color: #64748b; }
+
+    /* ── FLAG cases: colored side-tab borders using modern color formats ── */
+
+    /* 1: oklch border-left + border-radius (the canonical real-page bug) */
+    #flag-oklch-1 {
+      width: 400px;
+      background: oklch(100% 0 0);
+      border-radius: 4px;
+      border-left: 3px solid oklch(65% 0.12 250);
+    }
+
+    /* 2: oklch mixed — neutral 1px border all around + colored 4px left +
+          border-radius (mirrors .medication-card from the reproducer) */
+    #flag-oklch-2 {
+      width: 400px;
+      background: oklch(100% 0 0);
+      border: 1px solid oklch(80% 0.05 250);
+      border-left: 4px solid oklch(75% 0.15 45);
+      border-radius: 4px;
+    }
+
+    /* 3: oklch alert pattern — colored 4px border-left + border-radius */
+    #flag-oklch-3 {
+      width: 400px;
+      background: oklch(98% 0.01 60);
+      border-left: 4px solid oklch(75% 0.18 45);
+      border-radius: 4px;
+    }
+
+    /* 4: oklab border-left + border-radius */
+    #flag-oklab-1 {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 6px;
+      border-left: 4px solid oklab(60% 0.1 0.15);
+    }
+
+    /* 5: lch border-left + border-radius */
+    #flag-lch-1 {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 6px;
+      border-left: 4px solid lch(55% 60 250);
+    }
+
+    /* 6: lab border-left + border-radius */
+    #flag-lab-1 {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 6px;
+      border-left: 4px solid lab(50% 40 -30);
+    }
+
+    /* 7: card-shaped <label> with colored oklch side border + radius
+          (the checklist-item pattern from preop-portal reproducer) */
+    label#flag-label-oklch {
+      display: grid;
+      grid-template-columns: auto 1fr;
+      width: 400px;
+      padding: 16px;
+      background: oklch(100% 0 0);
+      border-radius: 4px;
+      border-left: 3px solid oklch(65% 0.12 250);
+      cursor: pointer;
+    }
+
+    /* 8: card-shaped <label> with colored rgb side border + radius —
+          proves the fix is not oklch-specific */
+    label#flag-label-rgb {
+      display: block;
+      width: 400px;
+      padding: 16px;
+      background: #ffffff;
+      border-radius: 6px;
+      border-left: 4px solid #3b82f6;
+      cursor: pointer;
+    }
+
+    /* ── PASS cases: legitimate or neutral borders, must NOT fire ── */
+
+    /* 1: oklch chroma ~0 — true neutral gray border should not fire */
+    #pass-oklch-neutral {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 3px solid oklch(80% 0 0);
+    }
+
+    /* 2: oklch low chroma (0.01) — still perceptually neutral */
+    #pass-oklch-nearneutral {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 3px solid oklch(75% 0.01 250);
+    }
+
+    /* 3: oklch colored border all around (not one-sided) — no side-tab */
+    #pass-oklch-allsides {
+      width: 400px;
+      background: #ffffff;
+      border: 3px solid oklch(65% 0.12 250);
+      border-radius: 4px;
+    }
+
+    /* 4: oklch colored 1px border-left (too thin to qualify) */
+    #pass-oklch-thin {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 1px solid oklch(65% 0.12 250);
+    }
+
+    /* 5: lab neutral (chroma near zero) — must not fire */
+    #pass-lab-neutral {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 3px solid lab(50% 0 0);
+    }
+
+    /* 6: lch neutral (chroma 0) */
+    #pass-lch-neutral {
+      width: 400px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 3px solid lch(50% 0 0);
+    }
+
+    /* 7: plain inline form label — no border, no padding, no radius.
+          Must NOT be flagged for anything. */
+    label#pass-label-plain {
+      font-size: 14px;
+      font-weight: 500;
+      color: #374151;
+    }
+
+    /* 8: form label with a small neutral gray left border — neutral color
+          should not fire the colored side-tab rule. */
+    label#pass-label-neutral-border {
+      display: block;
+      width: 400px;
+      padding: 8px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 3px solid #e5e7eb;
+    }
+
+    /* 9: inline label inside a form row — default inline layout,
+          no borders, must not fire. */
+    label#pass-label-inline {
+      font-size: 13px;
+      color: #6b7280;
+      margin-right: 8px;
+    }
+
+    /* 10: label with 1px colored left border — too thin to qualify
+          (matches the existing 1px thin rule for divs). */
+    label#pass-label-thin {
+      display: block;
+      width: 400px;
+      padding: 8px;
+      background: #ffffff;
+      border-radius: 4px;
+      border-left: 1px solid #3b82f6;
+    }
+  </style>
+</head>
+<body>
+  <div class="grid">
+    <div class="col" data-col="flag">
+      <h2>Should flag</h2>
+      <div class="case" id="flag-oklch-1"><h3>oklch checklist</h3><p>oklch border-left 3px + radius</p></div>
+      <div class="case" id="flag-oklch-2"><h3>oklch medication card</h3><p>neutral all + colored left 4px</p></div>
+      <div class="case" id="flag-oklch-3"><h3>oklch alert</h3><p>warm border-left 4px + radius</p></div>
+      <div class="case" id="flag-oklab-1"><h3>oklab card</h3><p>oklab border-left 4px + radius</p></div>
+      <div class="case" id="flag-lch-1"><h3>lch card</h3><p>lch border-left 4px + radius</p></div>
+      <div class="case" id="flag-lab-1"><h3>lab card</h3><p>lab border-left 4px + radius</p></div>
+      <label class="case" id="flag-label-oklch">
+        <input type="checkbox">
+        <span>Card-shaped label with oklch side border</span>
+      </label>
+      <label class="case" id="flag-label-rgb">
+        <input type="checkbox">
+        <span>Card-shaped label with rgb side border</span>
+      </label>
+    </div>
+    <div class="col" data-col="pass">
+      <h2>Should pass</h2>
+      <div class="case" id="pass-oklch-neutral"><h3>oklch neutral</h3><p>chroma 0 gray</p></div>
+      <div class="case" id="pass-oklch-nearneutral"><h3>oklch near-neutral</h3><p>chroma 0.01</p></div>
+      <div class="case" id="pass-oklch-allsides"><h3>oklch all sides</h3><p>uniform border</p></div>
+      <div class="case" id="pass-oklch-thin"><h3>oklch thin</h3><p>1px too thin</p></div>
+      <div class="case" id="pass-lab-neutral"><h3>lab neutral</h3><p>chroma 0</p></div>
+      <div class="case" id="pass-lch-neutral"><h3>lch neutral</h3><p>chroma 0</p></div>
+      <div>
+        <label for="pass-email" id="pass-label-plain">Email address</label>
+        <input type="email" id="pass-email">
+      </div>
+      <label id="pass-label-neutral-border">
+        <input type="checkbox">
+        <span>Label with neutral gray left border</span>
+      </label>
+      <form>
+        <label for="pass-name" id="pass-label-inline">Name:</label>
+        <input type="text" id="pass-name">
+      </form>
+      <label id="pass-label-thin">
+        <input type="checkbox">
+        <span>Label with 1px colored left border (too thin)</span>
+      </label>
+    </div>
+  </div>
+  <script src="/js/detect-antipatterns-browser.js"></script>
+</body>
+</html>