"White Out" typewriter correction fluid has worked well for my for 25 years. I like two things about it
1. It's cheap and dead flat, reflecting virtually no light...most paint that I've tried has glare which is counterproductive to accuracy. White out also works well if you hunt with iron sighted rifles....Makes that front sight jump right out at you at dusk or dawn.
2. You can get rid of the white out by chipping it off with a finger nail if for any reason you want black sights again. It even works on S&W's red plastic inserts on the big Magnums. I find that the red insert just reflects glare from the sky in actual woods use. White out shows up well against squirrel or deer hair too.
JMHO, Rodfac