After checking on the net, it seemed like all aircraft prior to november 1941 had RLM02 interior colour, so I gave the interior a cote of that colour.
Then I painted some details black.

I then added some more details in grey, reddish brown and white, and some belts made from tape and painted.

I’ll add some wash and drybrush a lighter tone of the interior green. I’ll also touch up the instrument panel and see if I can add some more colour to it. Once done, I’ll start closing the fuselage.