I've only done touch ups to Red and Green kettles and I can tell you for a fact that the spots on the bowls will eventually turn black. The lids on the other hand have stood up very well. My go-to paint is Dupli-Color Engine paint with Ceramic and the Red is a pretty good match. I'm more concerned with cosmetics and keeping the rust at bay on the lids where its more noticeable, the bowls just take too much heat.
Here's a couple examples of Seattle area Redheads that had rust damage that undermined the porcelain finish.
Mask the areas off as close to the damaged areas as possible.
I suppose if you were in the sandblasting business you could repaint a kettle any color you wanted to.
I've used Stove Brite fireplace paint that is supposed to be rated at 1200* on some Drum Smokers and accidentally left the lids off and had that paint burn off like nothing flat, so in the long run it wasn't worth spending $15+ a can.
Here is a pic of a Cajun Bandit conversion that I repainted a couple years ago that is starting to show some paint bleed through, but it kinda matches the two toned lid in a way.
your mileage may vary!