If it's the Airfix 1/24th scale Stuka, then the interior colour was predominantly RLM 02. However, there was a shade of paint, used particularly by Junkers, which was between RLM 02 and RLM66, seen on the Ju88. This was a sort of mid grey, a touch lighter than Humbrol grey 27. See Wayne's Ju88 thread, and the real '88 in Guttorm's posts.