I just use a white paint marker. The kind you shake, then push down on an object to get the felt tip to fill with enamel paint.
Simple black marker with a medium point to get into the dot recess. Never a problem.
For me, white/black contrast works best because of spectrum wash-out in nature. In other words, there are relatively few pure white or pure black backgrounds. So, in theory, a contrast of stark black/white might be better for many people.
or, I could be totally wrong, too.