Unless you have good evidence to the contrary you need a match for RLM02 which is indeed a green/grey colour.
Ray there really was no set switch over. Many bombers rolled off the junkers line with 66 interiors in early 1940. There is a suspicion that some Heinkel aircraft were painted this way before the war! There are pictures of downed Bf109s in 1940 where at least the area above the cockpit sills is in a dark colour,presumably RLM66. 109Es that had been damaged and significantly repaired also seem to have gained darker interiors in 1940,this maybe down to which contractor (Fiesler,Arado etc) did the work.
Nevertheless,if you don't have any firm evidence,RLM02 was still the officially designated interior colour for 109Es. The F series seem to have appeared with the RLM66 interiors common to all Luftwaffe fighters from that time on.
Dave Wadman wrote an excellent article detailing his extensive research into this area which I think is online somewhere but I can't seem to find a link to it.
Cheers
Steve