The GM Heritage Center info is a great resource. See Link. It's a free download.
The page about 1965 C10, C20 and C30 wheel colors has a short paragraph that says if your truck was a solid color or a black/off white two tone, then the wheels were black (you know that already). However, if the paint was two tone other than black, the wheels were the primary color.
The paint chip page says
BLACK
Option Numbers
Solid . . . 500
Two-Tone . . .530
Link to Heritage Center Info (click the word "show" next to Chevrolet Trucks)
http://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html
