There are a variety of projects here n home talk with tips for painting tiles https://www.hometalk.com/search/posts?filter=paint%20floor%20tiles
I would use a paint that's meant for tile, like this: https://amzn.to/2Z6NQMx. You'll want to make sure you use a strong paint that will hold up well under foot traffic.
You could also do something fun with a stencil, if you're not too concerned with it flaking off: https://amzn.to/2KGt1zy
Depending on how high traffic the area is, my guy at Sherwin Williams said they make an industrial floor epoxy paint and that is the only thing he would use on a high traffic area such as kitchen or widely used bathroom. I know Rustoleum makes one too! Maybe ask at your local HomeDepot!