Thank you for the replies! That procedure looks very difficult. I suppose I can get my watchmaker to do that.
.....
It's not too difficult, the skills that you need is to handle a small paint brush. Let me propose you a procedure that will keep
you "safe" and create a stronger result.
a) Find a photo that compares gen vs rep bezel.
b) Show it to a car paint shop or a graffiti paint cans shop, to decide the "right" tone of silver.
c) Protect the crystal and the rest of watch with masking tape. It's not a need, just for your piece of mind. Do not disasseble anything.
d) Make a small quantity of strong digreaser (for dishes or engine use) and use an ear stick to wash inside the markers as good as you can.
This is a critical step to create the "perfect" bond for your paint.
e) Apply the paint inside with a small paint brush. Don't mind if you have excess paint around them.
f) Let it dry for an hour and rub bezels' surface with a small (straight) piece of wood wrapped with thin cloth to clean the excess of color.
You've donne it! Blow air to clean them if needed. You can get it wet occassionaly but don't wear it in the sea.