My experts on stains say that Lambrusco stains tile and only costs about $10 for a couple of liters. The cheaper the better both for drinking and staining. Kool-Ade is costs more but alone leaves a sticky spot and you may lose some of the color when you wash it. It sticks better if the kids throw up soon after drinking some. If you have young kids, you will learn about McDonald's Shamrock Shakes on your own. Other than those, not much will stain your tiles.
I was going to make a comment about Sherry, since I mentioned the Lambrusco, but I better not.