I figure I'm either a genius or a complete fool.
My kitchen was remodeled a few years ago. I loved everything about it with the exception of the grout in the backsplash--it was much too dark and created a busy look. Now I know that's a small nitpicking thing in the grand scheme of life, but it annoyed me. Because there's the Internet and basically anything you need to know is there (as well as a huge amount of disinformation and a huge amount of things no one needs to know) I did a search on changing grout color. Advice ranged from redoing the grout with grout colorant to getting a power tool that removes all the grout then regrouting the whole thing. I was not going to use a toxic oil-based material in my house and I was not going to scrape it all out and do it again.
One little thing I saw on eHow mentioned using flat water-based paint. I'm addicted to flat water-based paint--I've painted so much furniture with Annie Sloan Chalk Paint that I've lost count. So I tried it. I mixed some Old White with water then started applying the paint wash to the grout with a brush. The grout sucked in the lighter color and the paint easily washed off of the glazed tile with a wet rag.
It now looks the way it should have looked in the beginning and I love it. And it took less than an hour to do. The lighter grout shows off the beautiful texture of the hand-made tiles so much more than the dark grout. Of course, maybe I'll end up being a fool in the long run if I find the grout gets discolored or mildewed or falls out because I had the nerve to paint it.
The photo of the corner is a little hint of before and after. The other photos show some of it finished.