Have you started on the kit yet?
I have just finished the Revell version and I'm having the same problems with the colour scheme.

The thread posted here haas given me some idea, but i'm inclined to go with RLM 76 for the underside, considering the coloring of other german planes in WWII. could be i'm wrong for the Spanish War period.

Ergo: after some more searching I found that RLM 65 was being used mostly untill 1943, after 1943 RLM 76 was mostly used.