1 cup paint + 2 Tablespoons non-sanded tile grout = homemade chalkboard paint in any color under the rainbow. The grout came from Home Depot, $4.97 for 5lbs (that's more than you realize) and I bought an "Oops" sample also from HD for 50 cents. The sample is actually 7.25oz. but it's enough and a great way to keep the mess down as well as it comes in a plastic screw lid container. Great for keeping the excess. I think on this project I used about 1/3 of the cup. One coat. Thinnner is better.
What an excellent idea. Hugs Mrs A.