add to the posts above, the original "hard rubber" (plastic) grips started with the Single Sixes, 1954-55 then the 357 mag flatops came out in 1955 had them,,,these 'hard rubber' grips, would often change colors , turn mainly brown, various shades and we've seen some almost green, this is a reaction from ultraviolet light ( sunlight) if a gun was out in the open, setting on a shelf or hanging on a wall or even in the holster hanging up the out side grip or in the case of one in the box or laying down,,,the exposed grip ( facing up or outward) turned color first....you can usually just oil or wipe them down with oil or even grease I use RIG myself and they will darken up if not then some folks used RIT Dye ( black) and soaked their grips, either way works I never used the dye, and often if they "match" both panels, leave 'em be, its like a badge of time and honor...looks good
yes old grips , wood or whatever material ,over time do "dry out" and need to be tended to........on stags and ivory we use lanolin, rub it in.........
again, 'welcome' Pecos Jake.............would love to see a picture of your gun