I have used a very small amount of Flitz polish on a Q-tip, but go lightly. It's a thin coating and a heavy hand could ruin it. I've also tried some Hoppe's 9 on them, that takes the oils and gunk off and works pretty well. If its a shooter, they'll darken up again quickly. I try the Hoppe's before I resort to the Flitz. I've not tried a wax/cleaner, I'm sure you'll hear more suggestions.
I would try Renn wax first.. Although a wax, I have had it clean a little and it will be the least harsh..it will cause no harm if it doesn't work. Flitz will work. Like the Chief said, careful and cautious. Q-tip. Light rub. Clean off Repeat until clean. Don't over scrub....you can put the scrub back in the medallion once its had too much of it.
With few exceptions later in production in the 1990's, all Python medallions were Gold.
It's not unusual to see Pythons with the original grips switched for grips made for other models that used Silver medallions.
If the grips are any of the original Colt Target First, Second, or Third Type walnut Target grips, the medallions would have been Gold, never Silver.
Silver was only used in the mid to later 1990's on rubber grips, the very last Python Elite finger groove grips, and on a very few special limited edition Pythons.
So, if your Python has Silver medallions, either the grips aren't original or the finish has worn badly.
A good jewelery store that does ring work on-site can gold or rhodium plate the medallions.
Even if they offer silver plating, don't. Silver tarnishes too badly. Rhodium plating is silver and won't tarnish.
Note that removal of medallions is risky and can crack the grips if not done correctly and carefully.
Cost for plating depends on the store.