rgbcomp.icn: Procedures to perform computations on RGB values

link rgbcomp
January 14, 1995; Ralph E. Griswold
Requires: Version 9 graphics
This file is in the public domain.

rgbsum(s1, s2) returns a color whose RGB components are the sums of the
components for s1 and s2.

rgbdif(s1, s2) returns a color whose RGB components are the differences of
the components for s1 and s2.

rgbavg(s1, s2) returns a color whose RGB components are the averages of
the components for s1 and s2.

rsgcomp(s) returns the color that is the complement of s.

The results may not be what's expected in some cases.