Yesterday when I was shooting my M&P9c the front suddenly got harder to see. I thought it was just dirty but when I got home I discovered the white ring around the tritium capsule was gone. Looking more closely it appears the white rings are just paint. Is that correct?

If so, what type of paint could I use to put the ring back on the front sight. Conversely, what could I use to take the paint off the rear sight to de-emphasize those rear dots?

Thanks for your help.