Cleaning hour markers

[Racer X]

Hi all,

Been looking at various vintage subs and many have discolored hour markers. I'm talking about the dark stains that look like mold or mildew. Sometimes they are a black color; other times they are brownish orange color. I'm wondering, is there any way to clean the hour markers to remove or lighten those stains? I was thinking maybe a q-tip soaked with a very mild bleach/water solution might clear them up. I, of course, would like to hear from the experts before trying something like this on a vintage timepiece.

Thanks.