One easy way to recycle leftover paint in myriad colors is to simply mix it 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 it into one large bucket and stir until it's completely blended. Add a few tablespoons of powdered grout from the hardware store and mix again. Voila! Instant chalkboard paint.