Testors red and white work well at duplicating the color used in the safety markings on Walthers and other guns. Their white is also good for sights that have white in lines or holes.
For plain paintng of sights, though, I recommend fingernail polish as there is a lot of variety and you can try several different colors at moderate cost. Also, fingernail polish is easy to remove without damage to the finish, unlike paint.
Jim