sometimes simply wiping the grips down with a good oil, we use 'RIG" on most guns that are handled often, and it will darken the polymers of the grip...as TY noted above it depends mainly on the ultraviolet lights and the LACK of ANY oils used to keep things from drying out..........we used to see this often on guns that would be hung on a wall , the grip facing out is lightened/faded. and the back one will still be dark......... 8) :roll: :wink: