Takes a hex color and luminosity adjustment and outputs new color

lightenDarkenColor.js

/* eslint-disable no-bitwise */

export default (inputColor, amt) => {
  let usePound = false
  let color = inputColor
  if (color[0] === '#') {
    color = color.slice(1)
    usePound = true
  }

  const num = parseInt(color, 16)

  let r = (num >> 16) + amt

  if (r > 255) r = 255
  else if (r < 0) r = 0

  let b = ((num >> 8) & 0x00FF) + amt

  if (b > 255) b = 255
  else if (b < 0) b = 0

  let g = (num & 0x0000FF) + amt

  if (g > 255) g = 255
  else if (g < 0) g = 0

  return (usePound ? '#' : '') + (g | (b << 8) | (r << 16)).toString(16)
}