Most British airplanes were painted a color called, "PC10" that gradually changed during the war. Go to the site mentioned above and do a search in the FORUM, in the MODELS section, for "PC10." You'll find some good information on what paints people are using for their models.
Two recommendations that I was able to find pretty quickly are: "Going through the colour chips in the Federal Standards 595a, there are 2 possibilities - F.S. 30117 and F.S. 30118. Testor makes both of them in their MM range. F.S. 30117 is Military Brown and F.S. 30118 is Field Drab, just a little bit darker than 30117."
That is quoted from this thread:
http://www.theaerodrome.com/forum/YaBB.cgi?board=models&action=display&num=1059969273&start=30
Regards,
-Drew