To deal with lining up black sights on black targets or red bulls eyes I start with ordinary white out. For example I brush a small dab on the top of the front sight post. This helps me distinguish it from the rear sight and the black or red target center. Especially on my guns that do not have a rear aperture sight. You can experiment with it and find out if you want a dab on the rear sight too. I start with white out because it is not permanent. If I don’t like it I can scratch it off with my finger nail. If you like the result and want to keep it then replace the white out with white nail polish.

My old eyes need all the help they can get too.