diff --git a/src/App.jsx b/src/App.jsx
index 88244e9..1c6b064 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -45,6 +45,7 @@ export default function App() {
   const [instrument, setInstrument] = useState('guitar')  // 'guitar' | 'piano'
   const [showTuner, setShowTuner]   = useState(false)
   const [showDebug, setShowDebug]   = useState(false)
+  const [monoColor, setMonoColor]   = useState(false)
 
   // ── Mic permission error ──────────────────────────────────────────────────────
   const [micError, setMicError] = useState(null)
@@ -306,6 +307,16 @@ export default function App() {
           <p className="text-xs text-gray-600">Real-time key detection for live jams</p>
         </div>
         <div className="flex gap-2 items-center">
+          <button
+            onClick={() => setMonoColor(v => !v)}
+            className={`p-2 rounded-full border transition-all ${monoColor ? 'border-accent bg-accent/10' : 'border-border hover:border-gray-400'}`}
+            title="Mono color mode"
+          >
+            <svg width="20" height="20" viewBox="0 0 20 20" fill="none" style={{ opacity: 0.75 }}>
+              <circle cx="6"  cy="10" r="4" fill={monoColor ? '#a855f7' : '#a855f7'} />
+              <circle cx="13" cy="10" r="4" fill={monoColor ? '#c084fc' : '#f59e0b'} />
+            </svg>
+          </button>
           <button
             onClick={() => setShowDebug(v => !v)}
             className={`p-2 rounded-full border transition-all ${showDebug ? 'border-accent bg-accent/10' : 'border-border hover:border-gray-400'}`}
@@ -474,8 +485,8 @@ export default function App() {
       <div className="flex gap-3 mb-3 items-stretch">
         <div className="w-full lg:w-[70%] min-w-0">
           {instrument === 'guitar'
-            ? <Fretboard keyInfo={effectiveKey} currentChord={currentChord} pentatonicOnly={false} />
-            : <Piano keyInfo={effectiveKey} currentChord={currentChord} />
+            ? <Fretboard keyInfo={effectiveKey} currentChord={currentChord} pentatonicOnly={false} monoColor={monoColor} />
+            : <Piano keyInfo={effectiveKey} currentChord={currentChord} monoColor={monoColor} />
           }
         </div>
 
diff --git a/src/components/Fretboard.jsx b/src/components/Fretboard.jsx
index 3ce7235..72eb399 100644
--- a/src/components/Fretboard.jsx
+++ b/src/components/Fretboard.jsx
@@ -30,14 +30,14 @@ const fretX = f => NUT_X + (f - 0.5) * FRET_W
 // y centre of string si (0 = high e, 5 = low E)
 const stringY = si => PAD_T + si * STRING_H
 
-function noteColor(isChordTone, isPenta, isScale) {
-  if (isChordTone) return { fill: '#a855f7', text: '#fff' }   // purple
-  if (isPenta)     return { fill: '#f59e0b', text: '#000' }   // amber
-  if (isScale)     return { fill: '#374151', text: '#d1d5db' } // grey
+function noteColor(isChordTone, isPenta, isScale, mono = false) {
+  if (isChordTone) return { fill: '#a855f7', text: '#fff' }
+  if (isPenta)     return mono ? { fill: '#c084fc', text: '#1e1b4b' } : { fill: '#f59e0b', text: '#000' }
+  if (isScale)     return mono ? { fill: '#e9d5ff', text: '#581c87' } : { fill: '#374151', text: '#d1d5db' }
   return null
 }
 
-export default function Fretboard({ keyInfo, currentChord, pentatonicOnly = false }) {
+export default function Fretboard({ keyInfo, currentChord, pentatonicOnly = false, monoColor = false }) {
   const { root, mode } = keyInfo ?? {}
 
   if (!root) return null
@@ -120,7 +120,7 @@ export default function Fretboard({ keyInfo, currentChord, pentatonicOnly = fals
           {STRINGS.flatMap((str, si) =>
             Array.from({ length: NUM_FRETS }, (_, fi) => {
               const pc = (str.root + fi) % 12
-              const color = noteColor(chordSet.has(pc), pentaSet.has(pc), scaleSet.has(pc))
+              const color = noteColor(chordSet.has(pc), pentaSet.has(pc), scaleSet.has(pc), monoColor)
               if (!color) return null
 
               const cx = fi === 0 ? OPEN_X : fretX(fi)
@@ -147,8 +147,8 @@ export default function Fretboard({ keyInfo, currentChord, pentatonicOnly = fals
 
       <div className="mt-3 flex gap-5 text-xs text-gray-500">
         <span><span className="text-accent">●</span> Chord tone</span>
-        <span><span className="text-amber-400">●</span> Pentatonic</span>
-        <span><span className="text-gray-500">●</span> Scale</span>
+        <span style={{ color: monoColor ? '#c084fc' : '#f59e0b' }}>●</span><span> Pentatonic</span>
+        <span style={{ color: monoColor ? '#e9d5ff' : '#6b7280' }}>●</span><span> Scale</span>
       </div>
     </div>
   )
diff --git a/src/components/Piano.jsx b/src/components/Piano.jsx
index 17dc4a2..731c09a 100644
--- a/src/components/Piano.jsx
+++ b/src/components/Piano.jsx
@@ -28,16 +28,16 @@ const BLACK_H    = 82         // black key height
 const LABEL_Y    = KEY_H - 10 // y of note label on white key
 const BLACK_LABEL_Y = BLACK_H - 8
 
-function keyColor(isChordTone, isPenta, isScale, isBlack) {
+function keyColor(isChordTone, isPenta, isScale, isBlack, mono = false) {
   if (isChordTone) return { fill: '#a855f7', text: '#fff' }
-  if (isPenta)     return { fill: '#f59e0b', text: '#000' }
-  if (isScale)     return { fill: '#374151', text: '#d1d5db' }
+  if (isPenta)     return mono ? { fill: '#c084fc', text: '#1e1b4b' } : { fill: '#f59e0b', text: '#000' }
+  if (isScale)     return mono ? { fill: '#e9d5ff', text: '#581c87' } : { fill: '#374151', text: '#d1d5db' }
   return isBlack
     ? { fill: '#1f1f1f', text: '#6b7280' }
     : { fill: '#f5f5f5', text: '#6b7280' }
 }
 
-export default function Piano({ keyInfo, currentChord }) {
+export default function Piano({ keyInfo, currentChord, monoColor = false }) {
   const { root, mode } = keyInfo ?? {}
   if (!root) return null
 
@@ -68,7 +68,7 @@ export default function Piano({ keyInfo, currentChord }) {
               const isChordTone = chordSet.has(k.pc)
               const isPenta     = pentaSet.has(k.pc)
               const isScale     = scaleSet.has(k.pc)
-              const { fill, text } = keyColor(isChordTone, isPenta, isScale, false)
+              const { fill, text } = keyColor(isChordTone, isPenta, isScale, false, monoColor)
               return (
                 <g key={`w-${oct}-${wi}`}>
                   <rect
@@ -102,7 +102,7 @@ export default function Piano({ keyInfo, currentChord }) {
               const isChordTone = chordSet.has(k.pc)
               const isPenta     = pentaSet.has(k.pc)
               const isScale     = scaleSet.has(k.pc)
-              const { fill, text } = keyColor(isChordTone, isPenta, isScale, true)
+              const { fill, text } = keyColor(isChordTone, isPenta, isScale, true, monoColor)
               return (
                 <g key={`b-${oct}-${bi}`}>
                   <rect
@@ -134,8 +134,8 @@ export default function Piano({ keyInfo, currentChord }) {
 
       <div className="mt-3 flex gap-5 text-xs text-gray-500">
         <span><span className="text-accent">●</span> Chord tone</span>
-        <span><span className="text-amber-400">●</span> Pentatonic</span>
-        <span><span className="text-gray-500">●</span> Scale</span>
+        <span><span style={{ color: monoColor ? '#c084fc' : '#f59e0b' }}>●</span> Pentatonic</span>
+        <span><span style={{ color: monoColor ? '#e9d5ff' : '#6b7280' }}>●</span> Scale</span>
       </div>
     </div>
   )