Yes, they are powder coated yellow.
So do you suggest to prime and paint it directly on the yellow? If yes I think that it will much easier...right?
Yes. I would sand the face of the rings but NOT to the metal - just to give it a bit more tooth and wipe it down with something like Xylene before priming and painting. Remember, Xylene is really toxic so make sure to wear gloves and a good respirator when using.