diff --git a/apps/api/src/__tests__/lib/branding/color-roles.test.ts b/apps/api/src/__tests__/lib/branding/color-roles.test.ts
index 7bea2d974..8eea51eba 100644
--- a/apps/api/src/__tests__/lib/branding/color-roles.test.ts
+++ b/apps/api/src/__tests__/lib/branding/color-roles.test.ts
@@ -251,3 +251,68 @@ describe("processRawBranding primary", () => {
     expect(profile.colors?.primary).toBe("#635BFF");
   });
 });
+
+describe("monochrome brands", () => {
+  const button = (background: string, textColor: string, index: number) => ({
+    index,
+    text: `Button ${index}`,
+    html: "",
+    classes: "",
+    background,
+    textColor,
+  });
+  const llmPicking = (primaryColor: string) => ({
+    ...emptyLlm,
+    buttonClassification: {
+      primaryButtonIndex: 0,
+      primaryButtonReasoning: "n/a",
+      secondaryButtonIndex: -1,
+      secondaryButtonReasoning: "n/a",
+      confidence: 0.9,
+    },
+    colorRoles: {
+      primaryColor,
+      accentColor: "",
+      backgroundColor: "#FFFFFF",
+      textPrimary: "#171717",
+      confidence: 0.8,
+    },
+  });
+
+  it("uses the black call to action when the chosen color is only a link color", () => {
+    const merged = mergeBrandingResults(
+      { colorScheme: "light", colors: {} },
+      llmPicking("#0072F5"),
+      [button("#171717", "#FFFFFF", 0), button("#FFFFFF", "#171717", 1)],
+    );
+    expect(merged.colors?.primary).toBe("#171717");
+    expect(merged.colors?.accent).toBe("#0072F5");
+  });
+
+  it("keeps a color that also fills a button", () => {
+    const merged = mergeBrandingResults(
+      { colorScheme: "light", colors: {} },
+      llmPicking("#0071E3"),
+      [button("#000000", "#FFFFFF", 0), button("#0071E3", "#FFFFFF", 1)],
+    );
+    expect(merged.colors?.primary).toBe("#0071E3");
+  });
+
+  it("keeps a navy call to action from replacing the brand color", () => {
+    const merged = mergeBrandingResults(
+      { colorScheme: "light", colors: {} },
+      llmPicking("#635BFF"),
+      [button("#0A2540", "#FFFFFF", 0)],
+    );
+    expect(merged.colors?.primary).toBe("#635BFF");
+  });
+
+  it("leaves dark pages alone", () => {
+    const merged = mergeBrandingResults(
+      { colorScheme: "dark", colors: {} },
+      llmPicking("#1ED760"),
+      [button("#111111", "#FFFFFF", 0)],
+    );
+    expect(merged.colors?.primary).toBe("#1ED760");
+  });
+});
diff --git a/apps/api/src/lib/branding/color-roles.ts b/apps/api/src/lib/branding/color-roles.ts
index 044fd2911..75402bbfb 100644
--- a/apps/api/src/lib/branding/color-roles.ts
+++ b/apps/api/src/lib/branding/color-roles.ts
@@ -32,6 +32,25 @@ export function isNearBlack(hex: string): boolean {
   return contrastYIQ(hex) < 40 && max < 140;
 }
 
+/** Near-black with no hue: a monochrome brand's black, not navy chrome. */
+export function isNeutralDark(hex: string): boolean {
+  const h = hex.replace("#", "");
+  if (h.length < 6) return false;
+  const channels = [0, 2, 4].map(i => parseInt(h.slice(i, i + 2), 16));
+  return isNearBlack(hex) && Math.max(...channels) - Math.min(...channels) < 30;
+}
+
+/** Straight-line RGB distance; Infinity unless both are #RRGGBB. */
+export function colorDistance(a?: string | null, b?: string | null): number {
+  const x = normalizeRoleHex(a);
+  const y = normalizeRoleHex(b);
+  if (!x || !y || x.length !== 7 || y.length !== 7) return Infinity;
+  const channels = (hex: string) =>
+    [1, 3, 5].map(i => parseInt(hex.slice(i, i + 2), 16));
+  const [p, q] = [channels(x), channels(y)];
+  return Math.hypot(p[0] - q[0], p[1] - q[1], p[2] - q[2]);
+}
+
 /** Chromatic brand color — not gray chrome, and not a near-black nav on light pages. */
 export function isUsableBrandPrimary(
   hex: string,
diff --git a/apps/api/src/lib/branding/merge.ts b/apps/api/src/lib/branding/merge.ts
index fa9e3ced5..90596ba01 100644
--- a/apps/api/src/lib/branding/merge.ts
+++ b/apps/api/src/lib/branding/merge.ts
@@ -1,5 +1,7 @@
 import { BrandingProfile } from "../../types/branding";
 import {
+  colorDistance,
+  isNeutralDark,
   isUsableBrandPrimary,
   normalizeRoleHex,
   shouldApplyLlmColorRoles,
@@ -318,6 +320,34 @@ export function mergeBrandingResults(
     }
   }
 
+  // Monochrome brands (black logo and calls to action, color only in links or
+  // artwork) have black as their primary color, which the chrome filters above
+  // reject on light pages. A near-black primary button is that signal, unless
+  // the chosen color also fills a button, as when a brand pairs a black call to
+  // action with colored ones.
+  const primaryFill = normalizeRoleHex(
+    merged.components?.buttonPrimary?.background,
+  );
+  const primaryColor = normalizeRoleHex(merged.colors?.primary);
+  if (
+    merged.colorScheme !== "dark" &&
+    primaryFill &&
+    isNeutralDark(primaryFill) &&
+    primaryColor &&
+    primaryColor !== primaryFill &&
+    !buttonSnapshots.some(
+      b =>
+        colorDistance(b.background, primaryColor) < 40 ||
+        colorDistance(b.borderColor, primaryColor) < 40,
+    )
+  ) {
+    merged.colors = {
+      ...merged.colors,
+      primary: primaryFill,
+      accent: merged.colors?.accent ?? primaryColor,
+    };
+  }
+
   if (llm.personality) {
     (merged as any).personality = llm.personality;
   }