Zane,
The interior color of the 37-38 pickups was a wrinkle brown. I have the color chips for the exterior commercial colors for 37-38 and there is no listing for this interior color. Jim Carter used to sell a brown wrinkle paint which, once applied, needed to be heated in order to wrinkle. I tried this on my 37 1/2 ton many years ago and I was not satisfied with the results--it wrinkled unevenly (and it was a real hassle trying to apply even heat in the entire cab). Eastwood came out with both brown and black wrinkle paint in spray cans and they worked really well (I redid my 37 with this paint)--BUT then they discontinued the brown wrinkle.
A couple years ago, I discovered a Rustoleum color, Autumn Brown, in their Textured Paint line. When it dries, it is VERY close to the original color (just a bit "brighter" I'd say). It has a texture similar to a wrinkle and does so evenly when it dries. Not PRECISELY like the original, but pretty darned close. It's the best I've seen currently available, and definitely without the hassle of the old Jim Carter paint. I'm currently using it on the interior door panels and dash of my 1938 panel truck--they're coming out very nicely.
I hope this helps.
Jim