Unlike Chevrolet Advance-Design trucks, GMC New Design trucks often/standard had their wheels painted a different color than the body color (large and small trucks).

Light-green wheels with dark-green body was one combination.

I think there might be information about this on Rob English's (pre-'60) GMC website: www.oldGMCtrucks.com

1950 1.5 & 2 ton photo from sales brochure