One easy way to recycle lots of leftover paint in a myriad of colors is to simply mix them all together into one, solid color of chalkboard paint. Make sure all the paint is water-based latex (most are these days) and in usable condition. Pour them all into one large bucket and stir until completely blended. Then add a few tablespoons of powdered grout (from the hardware store) and mix again. Voila! Instant chalkboard paint to use anywhere you want.