I have a Mod. 61-2 that is nickel plate with white plastic grips.
Question being were these grips checkered panels colored like wood from the factory?....
Long story-The grips looked terrible as they were off color scratched and had a overall dark reddish washed color as I polished them the smooth part of the grips came quickly to a nice ivory (old plastic yellowish) color but the molded checkered grip panels had this persistent splotchy irregular reddish hue in and on the groves of the checkering. I could have just polished it off but it would have ruined the checkering. After working through my collection of solvents that I knew didn't usually melt plastic I found one that worked along with a big handful of Q-Tips allowed me to clean all of this not molded into plastic reddish color from the grips which look great now for 1970's plastic. FYI-The plastic grips had shrunk some as I had to slightly enlarge the hole the cocking indicator stuck through as it would stick in the out position indicating the gun was cocked even though it wasn't cocked-not what anybody wants.

The nickel guns had the white grips. The blued guns had dark ones. Both had a contrasting color 'swirled' in them to look like marble or wood.

I just checked mine. The blue ones are dark brown with a blackish color swirled in.

The reddish coloration your white grips had may have come from storage in a gun rug. The Model 61's shipped in a blue box with a blue zippered pouch that had a red felt-like lining. It's possible the pouch got wet and the red color leeched onto the stocks.