Clean the area to be painted with Denatured Alcohol and a toothbrush just prior to painting it. Use a wooden toothpick to apply the paint in a few (2 or 3) thin layers rather than one heavy coat. Let the coats dry overnight before applying another coat. I would recommend Testor's Model paint in the 1 ounce jars. It comes in many colors, lasts a looooong time, and their Blaze Orange color works exceptionally well on front sights.
If there does come a day that you want so remove it, cut the thickened layers off with a new double edge razor blade, and use a bronze toothbrush and gun solvent to remove the remaining. paint. The point of an Exacto Knife will remove any stuck paint from the serrations. Works very well, and in fact I personally prefer this method to having a cut and plastic insert installed permanently into the front sight, as that can never be reversed, sometimes falls out and is more of a P.I.T.A. to repair.
I have done this to many of my revolvers and Colt Auto's and have had it on some of them for over 25 years. It withstands cleaning, gun powder blasts, and holster wear. If it does eventually start to wear a bit, just clean the painted area with Alcohol and re-apply another fresh coat. Your good to go for another bunch of years.
Chief38