Question about WWII era RAF test and evaluation markings

[upnorth]

Hello all:

I just bought one of RS Models' newly released 1/72 Avia B.534 biplane kits and am strongly considering painting it up in RAF test and evaluation markings.

Does anyone know what such markings would look like in a roughly 1939-1940 timeframe?

I'm assuming green/brown uppers and trainer yellow undersides, but what else to consider? What style of roundels to use, was the big "P" in the circle marking on the fuselage applicable or was that specifically for prototypes and not for foreign aircraft under evaluation?

Thanks in advance.