import colorsys


def _adjust_lightness(rgb_color, amount=0.6):
    """Adjust lightness of given RGB color."""
    hls = colorsys.rgb_to_hls(*rgb_color)
    new_color = (hls[0], max(0.0, min(1.0, amount * hls[1])), hls[2])
    return colorsys.hls_to_rgb(*new_color)