Rob,

There is no ID plate on the truck that would indicate the original color.

Here is GMC ID plate information for your year.

253
25 = 1 ton
3 = 137" wheelbase

22 = 228 engine

C = Oakland, CA

engine (head and block) casting code locations

information on interpreting GMC casting codes

Rob English's excellent oldGMCtrucks website

oldGMCtrucks.com discussion boards