I don't know for sure about Gretsch but Ludwig was willing to paint any color the customer wanted and I'd assume that to be competitive Slingerland and probably Gretsch were willing to do the same thing on a special order basis. This policy was probably mostly aimed at the school band market where schools would want drums in their colors but the service would have extended to other buyers as well. Most industrial paint users used DuPont Duco paint which was a fast drying industrial lacquer popular at the time. The seeming lack of a definitive list of colors in the catalogs might reinforce the "any color you want" theory but outside of Ludwig I haven't seen this mentioned specifically in a Gretsch catalog.