"Brown" Colt Hard Rubber Grips
Moralem, you mentioned your Colt Pocket Auto has original grips that turned brown. I used to carry these on a daily basis a couple of decades ago as they were reasonably priced, wonderful shooters, very accurate and totally reliable. They also were much easier to carry in our hot, humid climate than a 1911.
I once purchased one that had one pristine "black" grip -- the right one, and the left grip -- the one that would be next to the body on a right-handed shooter -- was brown. Couldn't figure it out, wondered if it had been exposed to sunlight for a long time somehow.
Then, I carried one with pristine original grips for MANY hours on an especially hot, steamy day, inside the waistband. Perspiration, etc. turned the left grip brown in just one day!! Horrified, I tried Armor-all on it, and it restored the original black finish. I then did the same with the other one with a "brown" inside grip, and it fixed it also. Hope this helps!
I noted all the rave reviews of the Remington 51. I admit, it is elegant and sleek as can be, but is a Pederson design and IMHO overly complicated. I had 2 in mint condition and both were jam-o-matics with perfect factory mags and factory ammo. Got rid of them both. There's a reason why Remington only sold (IIRC) about 60,000 of those and Colt sold ~535,000 .32 M1903's and another ~135,000 .380 Model M's (the colt factory designation for the 1903 Hammerless Pocket Auto.)
They are incredibly well-built guns, and it's hard for me to imagine that the new "Colt" repros will be as totally reliable, smooth and accurate as the originals...
Enjoy your fine pistols! They are truly a vestige of a wonderful era in American firearms manufacture that we'll never see again.
John