add one more variable (#25938)

static/app/components/performance/waterfall/utils.tsx

@@ -231,8 +231,9 @@ export const pickBarColour = (input: string | undefined): string => {
   const letterIndex1 = getLetterIndex(input.slice(0, 1));
   const letterIndex2 = getLetterIndex(input.slice(1, 2));
   const letterIndex3 = getLetterIndex(input.slice(2, 3));
+  const letterIndex4 = getLetterIndex(input.slice(3, 4));
 
   return colorsAsArray[
-    (letterIndex1 + letterIndex2 + letterIndex3) % colorsAsArray.length
+    (letterIndex1 + letterIndex2 + letterIndex3 + letterIndex4) % colorsAsArray.length
   ];
 };