(chultquist@smuts.uct.ac.za, student of Anthony Fairall), as part of his
Computer Science Honours project.  Works with Chromatek glasses,
which make red things look nearby, blue things far away.
New commands:
   chromadepth {on|off}
	replaces colors of points and polygons with depth-coded colors
   chromaparams ZSTART ZRANGE
	sets Z-range (distance from camera plane) over which
	colormapping applies.  Z=ZSTART maps to first entry,
	Z=ZSTART+ZRANGE maps to last entry in colormap.
   chromacmap  FILE.CMAP
	Specifies colormap.
See example files data/chromadepth.cmap and data/hipchroma.