diff --git a/src/index.html b/src/index.html
index 961617d..ae04e49 100644
--- a/src/index.html
+++ b/src/index.html
@@ -52,6 +52,28 @@
     .room-item.active { background: #4a90d9; color: #fff; }
     .room-item .area { font-size: 11px; opacity: 0.7; }
 
+    .theme-btn {
+      display: inline-block;
+      padding: 4px 10px;
+      margin: 2px 3px 2px 0;
+      border: 2px solid #ccc;
+      border-radius: 4px;
+      background: #fff;
+      cursor: pointer;
+      font-size: 12px;
+      line-height: 1.4;
+    }
+    .theme-btn.active { border-color: #4a90d9; }
+    .theme-swatch {
+      display: inline-block;
+      width: 12px;
+      height: 12px;
+      border-radius: 2px;
+      vertical-align: middle;
+      margin-right: 4px;
+      border: 1px solid rgba(0,0,0,0.15);
+    }
+
     #info {
       position: fixed;
       bottom: 16px;
@@ -74,6 +96,8 @@
     <div id="floor-buttons"></div>
     <h3>Rooms</h3>
     <div id="room-list"></div>
+    <h3>Theme</h3>
+    <div id="theme-buttons"></div>
   </div>
 
   <div id="info">Click a room to select it. Click furniture to edit. Scroll to zoom, drag to orbit.</div>
@@ -90,6 +114,7 @@
     import { HouseRenderer } from './renderer.js';
     import { DesignState } from './state.js';
     import { InteractionManager } from './interaction.js';
+    import { ThemeManager } from './themes.js';
 
     const viewer = document.getElementById('viewer');
     const houseRenderer = new HouseRenderer(viewer);
@@ -97,6 +122,7 @@
     let selectedRoom = null;
     let designState = null;
     let interaction = null;
+    let themeManager = null;
 
     houseRenderer.loadHouse('../data/sample-house.json').then(async (house) => {
       document.getElementById('house-name').textContent = house.name;
@@ -117,8 +143,10 @@
         }
       });
 
+      themeManager = new ThemeManager(houseRenderer);
       buildFloorButtons();
       buildRoomList();
+      buildThemeButtons();
     }).catch(err => {
       document.getElementById('house-name').textContent = 'Error loading data';
       document.getElementById('info').textContent = err.message;
@@ -170,6 +198,23 @@
     viewer.addEventListener('roomclick', (e) => {
       selectRoom(e.detail.roomId);
     });
+
+    function buildThemeButtons() {
+      const container = document.getElementById('theme-buttons');
+      container.innerHTML = '';
+      for (const theme of themeManager.getThemes()) {
+        const btn = document.createElement('button');
+        btn.className = 'theme-btn' + (theme.id === themeManager.currentTheme ? ' active' : '');
+        btn.innerHTML = `<span class="theme-swatch" style="background:${theme.swatch}"></span>${theme.name}`;
+        btn.addEventListener('click', () => {
+          themeManager.applyTheme(theme.id);
+          document.querySelectorAll('.theme-btn').forEach(b => b.classList.remove('active'));
+          btn.classList.add('active');
+          buildRoomList(); // re-render room list since floor was rebuilt
+        });
+        container.appendChild(btn);
+      }
+    }
   </script>
 </body>
 </html>
diff --git a/src/themes.js b/src/themes.js
new file mode 100644
index 0000000..01e6b4f
--- /dev/null
+++ b/src/themes.js
@@ -0,0 +1,124 @@
+import { COLORS } from './renderer.js';
+
+const THEMES = {
+  default: {
+    name: 'Standard',
+    swatch: '#e8e0d4',
+    colors: {
+      wall: { exterior: 0xe8e0d4, interior: 0xf5f0eb },
+      floor: { tile: 0xc8beb0, hardwood: 0xb5894e },
+      ceiling: 0xfaf8f5,
+      door: 0x8b6914,
+      window: 0x87ceeb,
+      windowFrame: 0xd0d0d0,
+      grid: 0xcccccc,
+      selected: 0x4a90d9
+    },
+    scene: { background: 0xf0f0f0, ambientIntensity: 0.6, directionalIntensity: 0.8 }
+  },
+  modern: {
+    name: 'Modern',
+    swatch: '#f5f5f5',
+    colors: {
+      wall: { exterior: 0xf5f5f5, interior: 0xffffff },
+      floor: { tile: 0xe0e0e0, hardwood: 0xc4a882 },
+      ceiling: 0xffffff,
+      door: 0x333333,
+      window: 0xa8d4f0,
+      windowFrame: 0x666666,
+      grid: 0xe0e0e0,
+      selected: 0x2196f3
+    },
+    scene: { background: 0xfafafa, ambientIntensity: 0.7, directionalIntensity: 0.6 }
+  },
+  warm: {
+    name: 'Warm',
+    swatch: '#ddd0b8',
+    colors: {
+      wall: { exterior: 0xddd0b8, interior: 0xf0e8d8 },
+      floor: { tile: 0xb8a890, hardwood: 0x9b6b3a },
+      ceiling: 0xf5efe5,
+      door: 0x6b4423,
+      window: 0x8bc4e0,
+      windowFrame: 0x8b7355,
+      grid: 0xc8b8a0,
+      selected: 0xd48b2c
+    },
+    scene: { background: 0xf5efe5, ambientIntensity: 0.5, directionalIntensity: 0.9 }
+  },
+  dark: {
+    name: 'Dark',
+    swatch: '#3a3a3a',
+    colors: {
+      wall: { exterior: 0x3a3a3a, interior: 0x4a4a4a },
+      floor: { tile: 0x2a2a2a, hardwood: 0x5a4030 },
+      ceiling: 0x333333,
+      door: 0x5a4030,
+      window: 0x4080b0,
+      windowFrame: 0x555555,
+      grid: 0x444444,
+      selected: 0x64b5f6
+    },
+    scene: { background: 0x222222, ambientIntensity: 0.4, directionalIntensity: 1.0 }
+  },
+  scandinavian: {
+    name: 'Scandi',
+    swatch: '#f0ece4',
+    colors: {
+      wall: { exterior: 0xf0ece4, interior: 0xfaf6f0 },
+      floor: { tile: 0xe8ddd0, hardwood: 0xd4b88c },
+      ceiling: 0xffffff,
+      door: 0xc4a87a,
+      window: 0xc0ddf0,
+      windowFrame: 0xb0b0b0,
+      grid: 0xd8d8d8,
+      selected: 0x5b9bd5
+    },
+    scene: { background: 0xf8f6f2, ambientIntensity: 0.65, directionalIntensity: 0.7 }
+  }
+};
+
+/**
+ * ThemeManager — applies visual themes by mutating COLORS and re-rendering.
+ */
+export class ThemeManager {
+  constructor(renderer) {
+    this.renderer = renderer;
+    this.currentTheme = 'default';
+  }
+
+  applyTheme(themeId) {
+    const theme = THEMES[themeId];
+    if (!theme) return;
+    this.currentTheme = themeId;
+
+    // Mutate the shared COLORS object
+    Object.assign(COLORS.wall, theme.colors.wall);
+    Object.assign(COLORS.floor, theme.colors.floor);
+    COLORS.ceiling = theme.colors.ceiling;
+    COLORS.door = theme.colors.door;
+    COLORS.window = theme.colors.window;
+    COLORS.windowFrame = theme.colors.windowFrame;
+    COLORS.grid = theme.colors.grid;
+    COLORS.selected = theme.colors.selected;
+
+    // Update scene background and lights
+    this.renderer.scene.background.setHex(theme.scene.background);
+    this.renderer.scene.traverse(child => {
+      if (child.isAmbientLight) child.intensity = theme.scene.ambientIntensity;
+      if (child.isDirectionalLight) child.intensity = theme.scene.directionalIntensity;
+    });
+
+    // Clear cached materials/geometry and re-render to pick up new colors
+    this.renderer._clearFloor();
+    this.renderer.showFloor(this.renderer.currentFloor);
+  }
+
+  getThemes() {
+    return Object.entries(THEMES).map(([id, t]) => ({
+      id,
+      name: t.name,
+      swatch: t.swatch
+    }));
+  }
+}