Resolved. It appears that there is no longer need to add nv to the rule file - d.rast has -o option to overlay null values. -- View this message in context: http://osgeo-org.1560.n6.nabble.com/Visualising-null-values-with-r-colors-tp5024693p5024695.html Sent from the Grass - Users mailing list archive at Nabble.com.