I used a frosted light red nail polish. Seems to gather the light well because of the aluminum powder (or whatever it is) and provides good contrast with targets of opportunity... i.e., rocks & cowpies & even game & bullseyes.
Degrease the sight, dab it on, turn the gun upside down to allow it to drip away from the gun, when a little more than half-dry, strike it off to be even with the top of the sight, allow to dry thoroughly.
Lasts for a significant portion of forever.
Terry