It is hard to reconcile the difference in color of the two halves. The difference is greater than I would expect from simply carrying on one side. Perhaps the gun has laid on one side exposed to the sun or the dark side was lying on an oily rag. Another possibility is that one side has already been cleaned. A look at the inner surface of both grips might give us a better guess.

I do note that the picture of the right side seems to be more overexposed (based on the background) than the left side picture is.

Bob