# ppmm_value: r,g,b,a
0:     0,   0,   0,   0  # < 0 background
22500:   0, 255, 255, 255  # lightblue
30000:   0, 102, 204, 255  # blue
37500: 204,   0, 204, 255  # purple
45000: 255,  51, 255, 255  # pink
inf:  255, 255, 255, 255  # max enhancment = white