bigron and Dgiz,
Re: High Power grips. Anthony Vanderlinden, in his book "The Belgian Browning Pistols", on page 170 states that the typical prewar grip panel had a red paint backing so that the wood could not absorb moisture and rust the frame. This practice was discontinued during World War II, but was reintroduced by FN in the second part of the 1940's, after which the practice was abandoned.
The wartime wooden grips did not have the red paint backing. The third type of grip was the Bakelite, an early form of plastic.
Anthonys book is very good, and has taught me a great deal about FN pistols.
Just as a note of possible interest, my tangent sight/slotted frame High Power, sn: 44071 has the red painted grip interiors, and so does my postwar Austrian Police HP, sn: 9100 marked: LGK T.
Charles