diff --git a/frontend/src/test/sidebar.test.tsx b/frontend/src/test/sidebar.test.tsx
index b8422d0..b2b919b 100644
--- a/frontend/src/test/sidebar.test.tsx
+++ b/frontend/src/test/sidebar.test.tsx
@@ -150,7 +150,7 @@ describe('Sidebar section summaries', () => {
     expect(screen.queryByText(opsChannel.name)).not.toBeInTheDocument();
     expect(screen.queryByText(aliceName)).not.toBeInTheDocument();
 
-    const search = screen.getByPlaceholderText('Search...');
+    const search = screen.getByLabelText('Search conversations');
     fireEvent.change(search, { target: { value: 'alice' } });
 
     await waitFor(() => {
diff --git a/frontend/src/themes.css b/frontend/src/themes.css
index 1e7253c..bb728d5 100644
--- a/frontend/src/themes.css
+++ b/frontend/src/themes.css
@@ -696,3 +696,102 @@
 [data-theme='paper-grove'] ::-webkit-scrollbar-thumb:hover {
   background: linear-gradient(180deg, hsl(157 34% 46%), hsl(227 34% 52%));
 }
+
+/* ── Monochrome ("Workbench") ─────────────────────────────── */
+:root[data-theme='monochrome'] {
+  --background: 0 0% 98%;
+  --foreground: 0 0% 8%;
+  --card: 0 0% 100%;
+  --card-foreground: 0 0% 8%;
+  --popover: 0 0% 100%;
+  --popover-foreground: 0 0% 8%;
+  --primary: 0 0% 10%;
+  --primary-foreground: 0 0% 98%;
+  --secondary: 0 0% 96%;
+  --secondary-foreground: 0 0% 10%;
+  --muted: 0 0% 97%;
+  --muted-foreground: 0 0% 18%;
+  --accent: 0 0% 94%;
+  --accent-foreground: 0 0% 8%;
+  --destructive: 0 0% 18%;
+  --destructive-foreground: 0 0% 98%;
+  --border: 0 0% 72%;
+  --input: 0 0% 72%;
+  --ring: 0 0% 10%;
+  --radius: 0.2rem;
+  --msg-outgoing: 0 0% 92%;
+  --msg-incoming: 0 0% 98%;
+  --status-connected: 0 0% 12%;
+  --status-disconnected: 0 0% 24%;
+  --warning: 0 0% 22%;
+  --warning-foreground: 0 0% 98%;
+  --success: 0 0% 12%;
+  --success-foreground: 0 0% 98%;
+  --info: 0 0% 18%;
+  --info-foreground: 0 0% 98%;
+  --region-override: 0 0% 14%;
+  --favorite: 0 0% 10%;
+  --console: 0 0% 18%;
+  --console-command: 0 0% 8%;
+  --console-bg: 0 0% 96%;
+  --toast-error: 0 0% 96%;
+  --toast-error-foreground: 0 0% 12%;
+  --toast-error-border: 0 0% 70%;
+  --code-editor-bg: 0 0% 96%;
+  --font-sans: 'Inter', 'Segoe UI', sans-serif;
+  --font-mono: 'IBM Plex Mono', 'Cascadia Mono', 'SFMono-Regular', monospace;
+  --scrollbar: 0 0% 18%;
+  --scrollbar-hover: 0 0% 8%;
+  --overlay: 0 0% 6%;
+}
+
+[data-theme='monochrome'] body {
+  background: hsl(0 0% 98%);
+}
+
+[data-theme='monochrome'] .bg-card,
+[data-theme='monochrome'] .bg-popover {
+  background: hsl(0 0% 100%);
+}
+
+[data-theme='monochrome'] .bg-msg-outgoing {
+  background: hsl(0 0% 92%);
+  border-left: 2px solid hsl(0 0% 12% / 0.9);
+}
+
+[data-theme='monochrome'] .bg-msg-incoming {
+  background: hsl(0 0% 98%);
+  border-left: 2px solid hsl(0 0% 12% / 0.35);
+}
+
+[data-theme='monochrome'] .bg-primary {
+  background: hsl(0 0% 10%);
+}
+
+[data-theme='monochrome'] button {
+  border-radius: 0.2rem;
+  box-shadow: none;
+  filter: none;
+  transition:
+    background-color 0.12s ease,
+    color 0.12s ease,
+    border-color 0.12s ease;
+}
+
+[data-theme='monochrome'] button:hover {
+  transform: none;
+  box-shadow: none;
+  filter: none;
+}
+
+[data-theme='monochrome'] button:active {
+  transform: none;
+}
+
+[data-theme='monochrome'] ::-webkit-scrollbar-thumb {
+  background: hsl(0 0% 18%);
+}
+
+[data-theme='monochrome'] ::-webkit-scrollbar-thumb:hover {
+  background: hsl(0 0% 8%);
+}
diff --git a/frontend/src/utils/theme.ts b/frontend/src/utils/theme.ts
index c5320e6..20c9a01 100644
--- a/frontend/src/utils/theme.ts
+++ b/frontend/src/utils/theme.ts
@@ -22,18 +22,18 @@ export const THEMES: Theme[] = [
     swatches: ['#F8F7F4', '#FFFFFF', '#1B7D4E', '#EDEBE7', '#D97706', '#3B82F6'],
     metaThemeColor: '#F8F7F4',
   },
+  {
+    id: 'paper-grove',
+    name: 'Paper Grove',
+    swatches: ['#F7F1E4', '#FFF9EE', '#2F9E74', '#E7DEC8', '#E76F51', '#5C7CFA'],
+    metaThemeColor: '#F7F1E4',
+  },
   {
     id: 'cyberpunk',
     name: 'Cyberpunk',
     swatches: ['#07080A', '#0D1112', '#00FF41', '#141E17', '#FAFF00', '#FF2E6C'],
     metaThemeColor: '#07080A',
   },
-  {
-    id: 'high-contrast',
-    name: 'High Contrast',
-    swatches: ['#000000', '#141414', '#3B9EFF', '#1E1E1E', '#FFB800', '#FF4757'],
-    metaThemeColor: '#000000',
-  },
   {
     id: 'obsidian-glass',
     name: 'Obsidian Glass',
@@ -59,10 +59,16 @@ export const THEMES: Theme[] = [
     metaThemeColor: '#140F24',
   },
   {
-    id: 'paper-grove',
-    name: 'Paper Grove',
-    swatches: ['#F7F1E4', '#FFF9EE', '#2F9E74', '#E7DEC8', '#E76F51', '#5C7CFA'],
-    metaThemeColor: '#F7F1E4',
+    id: 'high-contrast',
+    name: 'High Contrast',
+    swatches: ['#000000', '#141414', '#3B9EFF', '#1E1E1E', '#FFB800', '#FF4757'],
+    metaThemeColor: '#000000',
+  },
+  {
+    id: 'monochrome',
+    name: 'Monochrome',
+    swatches: ['#FAFAFA', '#FFFFFF', '#111111', '#EAEAEA', '#8A8A8A', '#4A4A4A'],
+    metaThemeColor: '#FAFAFA',
   },
 ];