code: function shiftLuminosity (hue, shiftAmount, huePoints) {
    if (hue === 360) {
      hue = 0
    }
    const hueShift = nearestHue(hue, huePoints)
    const phi = PHI(hue, hueShift)
    if (phi === 0) {
      return hue
    }
    let newHue
    if (phi > 0) {
      newHue = hue + shiftAmount
    } else {
      newHue = hue - shiftAmount
    }
    return limit(newHue, 0, 360)
  }
docs: Shift perceived luminance towards or away from a specific max hue value