Factory colors (no charge) were a solid color, they will be illustrated in 1951 data book or folders.
http://www.flickr.com/photos/advance-design_parts_co/8131120023/in/set-72157631872034068Two-tone or special colors were available as noted in this salesman order book from 1950. This availability went back into the early 40's at least. There are no paint codes anywhere on these trucks for reference.
http://www.flickr.com/photos/advance-design_parts_co/8335509814/in/set-72157631872034068There are also details available for the pinstripe around the wheels and cab belt line in the GM heritage archive link (I think it is in the Tech Tips).
Some of the vendors also sell a small pamphlet with this information on the pinstripes as well. The cab interior is another topic in itself search for that one and you will find a wealth of codes, opinions and information. Other factory paint options did not become available until the 1954 models.
