Wood grips from Russia

Hello,
I just got some more grips from Russia and among them are a pair of Walther PP grips, they are made of wood with the Walther logo on the outside.
They were taken off a gun that was in cosmoline so they have become dark and not like the light color that were issued in.
My question is how does one safely restore them to their correct color and what product does anyone recommend.
Thank you much!
Der Hessian