The first Ju 87 B reached I./St.G. 162 in June 1938 and production of the A series ceased in August. The early B series aircraft seem to have had an RLM 02 interior. The B-2 prototypes were converted from A-1s in January 1939 and also had 02 interiors. By the end of March 1939 Junkers had delivered 187 B series aircraft and I believe all of them had 02 interiors. I also believe that aircraft delivered up to at least mid 1940 had 02 interiors, but there is some evidence of a darker interior, (presumably RLM 66) appearing around this time in some photographs. Whether this was factory applied or as a result of a refurbishment or overhaul I don't know.
Rather like the Bf 109 E I would suggest using an RLM 02 interior for aircraft produced up to, say, the BoB period unless you have compelling evidence to the contrary.
Even more confusing are photographs of Ju some 87 Ds with a light (02) interior at a date when this would be unexpected
As to my question of the colour of the IP...
"In the manual for the B series the instrument panel is RLM 02. The instruments themselves are, as you'd expect, a very dark colour, probably black. The various control boxes, radios etc vary so you have artistic licence! Most are a dark grey (66) or black. Something often missed is the frame of the bordfunker's seat. In all the pictures I have this is clearly a glossy black colour, not RLM 02."
As I will do an early BoB 87 I went for the 02 as the 66 might make for a difficult to detail "dark cave" cockpit...I have to re-do my IP as I made this 66 - darn.
Theuns