function getCacheKey(src, crossOrigin, color) {
  const colorString = color ? asArray(color) : 'null';
  return crossOrigin + ':' + src + ':' + colorString;
}
@param {string} src Src.
@param {?string} crossOrigin Cross origin.
@param {import("../color.js").Color|string|null} color Color.
@return {string} Cache key.