Detect text color for good contrast with background

appearance.ts

export function textColorForBackground(hexColor: string): 'white' | 'black' {
  let hex = hexColor.replace('#', '');
  let r = parseInt(hex.substr(0, 2), 16);
  let g = parseInt(hex.substr(2, 2), 16);
  let b = parseInt(hex.substr(4, 2), 16);

  let brightness = (r * 299 + g * 587 + b * 114) / 1000;

  return brightness > 155 ? 'black' : 'white';
}