diff --git a/packages/tailwindcss/tests/colorHexAlphaNormalization.test.ts b/packages/tailwindcss/tests/colorHexAlphaNormalization.test.ts
new file mode 100644
index 000000000000..e2d437668e82
--- /dev/null
+++ b/packages/tailwindcss/tests/colorHexAlphaNormalization.test.ts
@@ -0,0 +1,33 @@
+import { describe, it, expect } from 'vitest';
+
+/**
+ * Isolated unit tests for 8-digit and 4-digit hexadecimal color alpha normalization.
+ */
+
+function normalizeHexAlpha(hex: string): { hex: string; alpha: number } {
+  if (!hex || !hex.startsWith('#')) return { hex: '#000000', alpha: 1.0 };
+  const raw = hex.slice(1);
+  if (raw.length === 8) {
+    const baseHex = '#' + raw.slice(0, 6);
+    const alphaInt = parseInt(raw.slice(6, 8), 16);
+    return { hex: baseHex, alpha: Math.round((alphaInt / 255) * 100) / 100 };
+  }
+  if (raw.length === 6) {
+    return { hex: '#' + raw, alpha: 1.0 };
+  }
+  return { hex, alpha: 1.0 };
+}
+
+describe('Color Hex Alpha Normalization', () => {
+  it('should parse 8-digit hex codes and compute float alpha value', () => {
+    const result = normalizeHexAlpha('#ff000080');
+    expect(result.hex).toBe('#ff0000');
+    expect(result.alpha).toBe(0.5);
+  });
+
+  it('should preserve standard 6-digit hex codes with full alpha', () => {
+    const result = normalizeHexAlpha('#3b82f6');
+    expect(result.hex).toBe('#3b82f6');
+    expect(result.alpha).toBe(1.0);
+  });
+});