diff --git a/lib/colors.ts b/lib/colors.ts
index f9c0b5b0b..139cda23d 100644
--- a/lib/colors.ts
+++ b/lib/colors.ts
@@ -194,6 +194,7 @@ const colorMap: Record<string, string> = {
 }
 
 export function isDark(color: string = ''): boolean {
+  color = color.toLowerCase()
   // Equation from http://24ways.org/2010/calculating-color-contrast
   let rgb = colorMap[color] ? hexToRgb(colorMap[color]) : hexToRgb(color)
   const res = (rgb[0] * 299 + rgb[1] * 587 + rgb[2] * 114) / 1000