# ppmm_value: r,g,b,a
0:     0,   0,   0,   0  # < 0 background
1000: 96,  96,  224, 255  # darkblue
2000: 24, 224,    0, 255  # green
3000: 200, 224,   0, 255  # yellow
4000: 248,   0,  16, 255  # red
inf:  255, 255, 255, 255  # max enhancment = white