This is only possible if you specify multiple colormaps or scales (e.g., --colorMap Spectral summer or --yMin 0 1 2). Truth be told, you should be able to specify the same thing multiple times, such as --yMin 0 0 0 and get the same effect. Note however that I really wouldn't recommend that, as it both busies up the resulting plot and makes it less apparent that the scales are identical everywhere.