Friend had an old parkerized pistol that looked, well, bland. Dry. So gave it a short version of the process Xavier did: took the grips off, wiped it all over with grease and put it in the oven on 'warm' for a couple of hours and let it cool down, then wiped the excess off.
It almost looked refinished; the parking looked much better and more even, and darker. Says when has a chance he'll break the pistol down to remove all the springs and do the full procedure just to make sure the grease has a chance to soak all the way in.