Mine has deteriorated so its good to know that pulling it off is the solution.
I'll peel off the black coating and just replace the knob it in its original gray.
I don't believe a good physical bond of new paint will adhere long, because this button is used all the time.
An alternative would be to make a new style button out of wood, plastic, aluminium and using a little set screw to keep it in place.
No ! Don't Try to Pull it Off. IT DOESN'T PULL OFF !!! When I brought my 08 Pure 6 months ago it had the same issue with the black paint and the salesperson took a cloth with alcohol and a little elbow grease and took the remaining black paint off leaving a white/pearl knob that illuminates. Just work with it and you'll win. Happy Holidays.