rgbToHsv = (...values) => {
  values = flatten(values)
  if (values.length < 3) throw new Error('values must contain R, G and B values')

  const r = values[0]
  const g = values[1]
  const b = values[2]

  const max = Math.max(r, g, b)
  const min = Math.min(r, g, b)
  let h
  const v = max

  const d = max - min
  const s = max === 0 ? 0 : d / max

  if (max === min) {
    h = 0 // achromatic
  } else {
    switch (max) {
      case r:
        h = (g - b) / d + (g < b ? 6 : 0)
        break
      case g:
        h = (b - r) / d + 2
        break
      case b:
        h = (r - g) / d + 4
        break
    }
    h /= 6
  }

  if (values.length > 3) {
    // add alpha if provided
    const a = values[3]
    return [h, s, v, a]
  }
  return [h, s, v]
}
Converts an RGB color value to HSV.

@see http://en.wikipedia.org/wiki/HSV_color_space.
@param {...Number|Array} values - RGB or RGBA color values
@return {Array} HSV or HSVA color values
@alias module:modeling/colors.rgbToHsv