// brightness: 0 to 255
static int rgbIntFromGrayscale(int brightness) {
  brightness = clampToUByte(brightness);
  ret brightness | (brightness << 8) | (brightness << 16);
}

// brightness: 0 to 1
static int rgbIntFromGrayscale(double brightness) {
  ret rgbIntFromGrayscale(zeroToOneToZeroTo255(brightness));
}