@staticmethod
def next_colour(pix):
    """Move each colour along."""
    red = pix[0]
    green = pix[1]
    blue = pix[2]
    if red == 255 and green < 255 and blue == 0:
        green += 1
    if green == 255 and red > 0 and blue == 0:
        red -= 1
    if green == 255 and blue < 255 and red == 0:
        blue += 1
    if blue == 255 and green > 0 and red == 0:
        green -= 1
    if blue == 255 and red < 255 and green == 0:
        red += 1
    if red == 255 and blue > 0 and green == 0:
        blue -= 1
    pix[0] = red
    pix[1] = green
    pix[2] = blue
