According to the 1941 GMC Painting Specifications on the OldGMCTrucks.com website, wheels could be black OR the body color OR the stripe colorin accordance with the order form. (Most common is the wheels would be painted the stripe color)
There will be no additional charge or credit for either selection.

One other note regarding wheel painting/powdercoating. I have had a set of my wheels powdercoated in the past, and I will NEVER do that again. The areas around the bolt holes can build up the coating too thickly. The result is that when properly torquing the lugnuts you can damage the coating in this area. Further wear while driving can result in loose lugnuts. Unless you have special assurances from your powdercoater that he knows about this, I would strongly recommend a quality painting be done to the wheels instead of powdercoating. Touchups will be easier over the long haul as well. Just my opinion.