Green is easy on the eyes, and might compliment the yellow exterior... tan or brown would also sorta work. Flat black always looks like primer to me, as if the paint job was never completed. Perhaps a glossy grey for a more finished look?

1955 First Series GMC 250 1-Ton Panel
In the Gallery
Mr. Hedgehog - Follow the build
If you can't laugh at yourself, I'll laugh at you.