[Franek Grabowski]

Juha
It is simple question but the answer is both simple and complicated.
Polish aircraft of the period were painted in simple scheme of khaki and light blue grey for combat aircraft and overall khaki (mostly) or silver for trainers. Exception were Lublin observation aircraft which had a three tone camouflage and silver undersurfaces.
The problem is with actual shades used. Early PZL aircraft like P-11 or P-23 had a dark khaki fading into something similar to british Dark Earth and light blue comparable to RLM 76 fading into light grey. It is believed somewhere in 1937-38 paint formula changed and khaki turned slightly more greenish. It is confirmed both by colour photos of the aircraft and some bits of Los I have seen. I would compare the colour to the fresh WWII US Army Olive Drab.
Colour used on PWS was similar to the one of early PZL but a little bit lighter and perhaps not fading so strongly. There is no sample of RWD colours known to me. Generally I would say colours should be dark olive brown and light blue grey for a factory fresh aircraft.