diff --git a/crates/browser/tests/design_system_palette.rs b/crates/browser/tests/design_system_palette.rs
new file mode 100644
index 000000000..d1088841f
--- /dev/null
+++ b/crates/browser/tests/design_system_palette.rs
@@ -0,0 +1,138 @@
+//! `ai-color-palette` against a project's own documented palette, through a
+//! real browser.
+//!
+//! The FakeDom tests in `impeccable-core` pin the rule's decision; this one
+//! pins the thing only a browser can answer: that the `oklch()` a DESIGN.md
+//! declares and the `oklch()` Chrome computes for an element are the same
+//! color by the time the rule sees them. A `file://` target loads the
+//! DESIGN.md that governs the page's directory, so the whole path runs — the
+//! allowlist is parsed from the markdown, the page is rendered, and the
+//! browser element sweep decides.
+//!
+//! Skips cleanly without an installed browser or a built binary, the way
+//! `differential.rs` does.
+//!
+//! Env:
+//! - `IMPECCABLE_BIN` — the binary (default `target/debug/impeccable`).
+
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+use serde_json::Value;
+
+fn workspace_root() -> PathBuf {
+ Path::new(env!("CARGO_MANIFEST_DIR"))
+ .join("../..")
+ .canonicalize()
+ .expect("workspace root")
+}
+
+/// A DESIGN.md whose palette is all `oklch()`, including a verdigris that
+/// sits inside the rule's cyan band and a violet inside its purple one.
+const DESIGN_MD: &str = "---\n\
+name: Instruments\n\
+colors:\n\
+\x20 paper: \"oklch(97.8% 0 0)\"\n\
+\x20 ink: \"oklch(13% 0 0)\"\n\
+\x20 instrument: \"oklch(24% 0 0)\"\n\
+\x20 patina: \"oklch(70% 0.12 188)\"\n\
+\x20 iris: \"oklch(58% 0.2 300)\"\n\
+---\n\n\
+The palette above is the whole system.\n";
+
+fn page(swatch_color: &str, gradient: &str) -> String {
+ format!(
+ "\
+Instruments\
+\
+\
+Live\
+
\
+\
+"
+ )
+}
+
+fn rules(bin: &Path, dir: &Path, file: &str) -> Vec {
+ let url = format!("file://{}", dir.join(file).display());
+ let out = Command::new(bin)
+ .arg("detect")
+ .arg("--json")
+ .arg(&url)
+ .current_dir(dir)
+ .output()
+ .expect("run detect");
+ let stdout = String::from_utf8_lossy(&out.stdout).to_string();
+ let parsed: Value = serde_json::from_str(&stdout)
+ .unwrap_or_else(|e| panic!("detect {url} did not print JSON ({e}): {stdout}"));
+ parsed
+ .as_array()
+ .expect("findings array")
+ .iter()
+ .filter_map(|f| f.get("antipattern")?.as_str().map(str::to_string))
+ .collect()
+}
+
+#[test]
+fn ai_palette_respects_a_documented_oklch_palette() {
+ let env: HashMap = std::env::vars().collect();
+ if impeccable_browser::discovery::find_browser(&env).is_err() {
+ eprintln!("skip: no installed browser found");
+ return;
+ }
+ let bin = std::env::var("IMPECCABLE_BIN")
+ .map(PathBuf::from)
+ .unwrap_or_else(|_| workspace_root().join("target/debug/impeccable"));
+ if !bin.exists() {
+ eprintln!(
+ "skip: {} missing (cargo build -p impeccable, or set IMPECCABLE_BIN)",
+ bin.display()
+ );
+ return;
+ }
+
+ let dir = std::env::temp_dir().join(format!("impeccable-ds-palette-{}", std::process::id()));
+ std::fs::create_dir_all(&dir).expect("temp dir");
+ // A project marker, so the DESIGN.md walk-up stops here rather than
+ // climbing out of the temp directory.
+ std::fs::write(dir.join("package.json"), "{\"name\":\"ds-palette-fixture\"}\n").unwrap();
+ std::fs::write(dir.join("DESIGN.md"), DESIGN_MD).unwrap();
+ std::fs::write(
+ dir.join("declared.html"),
+ page(
+ "oklch(70% 0.12 188)",
+ "linear-gradient(oklch(58% 0.2 300), oklch(70% 0.12 188))",
+ ),
+ )
+ .unwrap();
+ std::fs::write(
+ dir.join("undeclared.html"),
+ page(
+ "rgb(0, 229, 255)",
+ "linear-gradient(rgb(168, 85, 247), rgb(59, 130, 246))",
+ ),
+ )
+ .unwrap();
+
+ let declared = rules(&bin, &dir, "declared.html");
+ let undeclared = rules(&bin, &dir, "undeclared.html");
+ let _ = std::fs::remove_dir_all(&dir);
+
+ // Every color on this page is a token the DESIGN.md declares, so neither
+ // the palette rule nor the drift rule has anything to say.
+ assert!(
+ !declared.iter().any(|r| r == "ai-color-palette"),
+ "declared tokens reported as a generic AI palette: {declared:?}"
+ );
+ assert!(
+ !declared.iter().any(|r| r == "design-system-color"),
+ "declared tokens reported as drift: {declared:?}"
+ );
+
+ // The same shapes in colors the DESIGN.md never declared still fire.
+ assert!(
+ undeclared.iter().any(|r| r == "ai-color-palette"),
+ "undeclared neon and violet gradient went unreported: {undeclared:?}"
+ );
+}