Micarta or G10 left "as finished" will get stained and discolored (light/dark) from handling and usage. My solution has been to put a light coat of Tru-oil on the handle, then immediately dry it off with a lint free rag or one of the blue "shop" paper towel. This works especially well with about a 220 grit finish, or even better with a light bead blasting. Once the Tru-Oil is applied/wiped off, I stab the knife into a block of foam on the bench and leave it set for at least 2 hours to dry. Prior to sending the knife out I carefully check to ensure there is no Tru-oil where I don't want it...if there is any clean up to do, I use a Q-Tip and acetone. Once the Tru-Oil is dry on the micarta/G10 the only way to remove it is with acetone or similar solvents.