What kind of paint would I use on plastic counters to make them visible to someone with visual impairment?

Hi. I am a carer for an elderly man who is losing his sight. He loves to play games and was very depressed today that we could not play othello because he could not see the black counters. He could see the white ones so am thinking of using some kind of bright paint to cover the black side. Any ideas?What kind of paint would I use on plastic counters to make them visible to someone with visual impairment?
Plasti-cote spray paint. Degrease/clean the counters beforehand.What kind of paint would I use on plastic counters to make them visible to someone with visual impairment?
Contrasting colours, day-glo green and orange contrast well. Red and blue.