Unknown colours were set to red previously but identified as black.  I have fixed that small inconsistency in name and updated the comment consistently.
Unknown colours were set to red previously but identified as black.  I
have fixed that small inconsistency in name and updated the comment
consistently.

svn path=/trunk/; revision=10315

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot