diff --git a/ui/desktop/index.html b/ui/desktop/index.html
index 2f03d59269..fc58a5900e 100644
--- a/ui/desktop/index.html
+++ b/ui/desktop/index.html
@@ -25,7 +25,11 @@
               // Apply custom theme colors if enabled
               const customThemeEnabled = localStorage.getItem('custom_theme_enabled') === 'true';
               if (customThemeEnabled) {
-                const customColor = localStorage.getItem('custom_theme_color') || '#32353b';
+                let customColor = localStorage.getItem('custom_theme_color') || '#32353b';
+                // Validate the color before applying it
+                if (!hexToRgb(customColor)) {
+                  customColor = '#32353b';
+                }
                 applyCustomThemeColors(customColor, isDark);
               }
             } else {
@@ -78,9 +82,9 @@
             const hue2rgb = (p, q, t) => {
               if (t < 0) t += 1;
               if (t > 1) t -= 1;
-              if (t < 1/6) return p + (q - p) * 6 * t;
-              if (t < 1/2) return q;
-              if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
+              if (t < 1/6) return p + (q - p) * 6 * t; // Hue in red-yellow range
+              if (t < 1/2) return q; // Hue in yellow-green range
+              if (t < 2/3) return p + (q - p) * (2/3 - t) * 6; // Hue in green-blue range
               return p;
             };
             const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
diff --git a/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx b/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx
index de1a50bb04..9c3c0422d8 100644
--- a/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx
+++ b/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx
@@ -3,7 +3,12 @@ import { Moon, Sliders, Sun, Palette, type LucideIcon } from 'lucide-react';
 import { Button } from '../ui/button';
 import { Switch } from '../ui/switch';
 import { CustomColorPicker } from './CustomColorPicker';
-import { applyCustomTheme, resetThemeColors, DEFAULT_THEME_COLOR } from '../../utils/colorUtils';
+import {
+  applyCustomTheme,
+  resetThemeColors,
+  DEFAULT_THEME_COLOR,
+  isValidHexColor,
+} from '../../utils/colorUtils';
 import { cn } from '../../utils';
 
 interface ThemeSelectorProps {
@@ -68,7 +73,10 @@ export function ThemeSelector({
       }
 
       if (e.key === 'custom_theme_color' && e.newValue) {
-        setCustomColor(e.newValue);
+        // Validate the color before setting it to state
+        if (isValidHexColor(e.newValue)) {
+          setCustomColor(e.newValue);
+        }
       }
 
       if (e.key === 'custom_theme_enabled') {