put back lost standard color names

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@44828 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.colors/r.colors.html

@@ -146,7 +146,8 @@ end
 
 <p>
 Each category value must be valid for the raster map layer, category values must
-be in ascending order and only use standard GRASS color names (see above).
+be in ascending order and only use standard GRASS color names (aqua, black, blue,
+brown, cyan, gray, green, grey, indigo, magenta, orange, purple, red, violet, white, yellow).
 
 <p>
 Colors can also be specified by color numbers each in the range 0-255. The