Well, I like your counters. They are interesting, neutral, and pretty easy to work with.

Are you sure you want to paint gray?

Note that gray comes in every shade from pale to dark. So, gray, in and of itself, won't make your kitchen dark. You can brighten your kitchen by improving lighting. Bright undercabinet lighting, and better overhead lighting will change the way the kitchen feels.

For biggest bang for the buck, look at installing some nice backsplash tile which can give your space a lot of personality.

I do know of a blogger I used to follow who painted her tile countertops as a temporary solution. I wouldn't do it, but at least you can see her process, and I have no idea if using the products she used is advisable on YOUR counters, but it's a place to start, and I'm sure you can google other blogs for further info. advice.http://www.livelovediy.com/2013/02/how-to-paint-tile-and-update-your.html

I think your counters are fine