Look up a color name. If it exists, return
the rgb value of the color. If it does not exist, look up the value
of the second argument, which should normally be "black" or "white".
All names are converted to lower case before looking them up.
If the global variable tyMonochrome is set, then use the second
argument (if it is present).
This procedure
is simply an interface to the class proc ::tycho::FontManager::getColor,
and is provided for convenience.