New color hack

[GLS at MIT-AI (Guy L. Steele, Jr.)]

CC: HES at MIT-AI, GLS at MIT-AI, DANNY at MIT-AI

An alternative to COLOR:COLORIZE is COLOR:COLORATE.  It repeatedly chooses
a random pair of colors and linearly "melts" them into each other; that is,
the colors are exchanged, but slowly, by a process of mutual linear
interpolation.  It is a nice effect.  It is especially good with
SPECTRUM-COLOR-MAP, which duplicates colors, because things seem to
fade away and then reappear (because it and its background are temporarily
the "same" color.)  I put this into LMIO;COLOR and recompiled.