Rustoleum or Homac tub and tile paint kits. Must be epoxy based.
Pick up a bonding adhesion primer, do a couple coats, paint over that then seal it up. You can see how I did a floor here: https://www.flippingtheflip.com/2019/03/how-to-stencil-paint-ceramic-tile-floor.html?m=1
Be sure to prime prime prime! I would personally use an oil based primer ( like this one) because it is more durable. Then when you go to paint, check with the paint company if you can use water based paint over an oil based primer, or if you will need to go with an oil based paint option.
Once you have painted, I would seal it to prevent any scratching, etc. I love a product called Gator Hide by Dixie Belle paint.
Here's an article that might help - https://brepurposed.porch.com/2017/09/21/paint-tile-backsplash/