optimize GDD colors

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@53224 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/gis/colors/gdd

@@ -3,7 +3,7 @@
 500 blue
 1000 green
 1500 yellow
-2500 red
-4000 brown
-5000 violet
+2000 red
+3000 brown
+3500 violet
 6000 50 0 0