I chose a yellow paint for the kitchen that is way too bright and bold. Is there anything I can paint over it to tone it down or should I prime and paint again?

Yellow is definately one of the hardest colors to get right. I suggest that you choose another color. Instead of going to the bright yellows, look at Benjamin Moore: HC-30 Philadelphia Cream, HC36, Hepplewhite Ivory (or some of the other colors on this color card). These are much softer yellows, almost butter yellow and will be much more soothing on the eye, but still nice and bright in the kitchen. Try painting a small piece of drywall and look at it before putting it on the wall. But don't look at it next to your bright yellow, it will distort the color!
Good luck :)
Kelli