Some people have had success with a product called Seaglow in the past but thats more or less for gum rubber to make it crystal clear again.... Yellowing is tricky, I used to try watered down acetone but its probably not the best idea. Hopefully someone else posts up another option soon however if its just a bit of white thinly on the rubber I wouldnt stress tonnes about painting it. I more or less assumed you wanted to recolor or paint it with a pattern etc.
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"Every child is an artist. The problem is how to remain an artist once he grows up" - Pablo Picasso