Simple plywood or medium-density fiberboard (MDF) panel and crafts paint. Sand and clean the wood panel, then use a pencil to mark off a grid of same-size squares. Arrange crafts paint in the same color palette from light to dark. Assign a color to each square, keeping lighter colors at the bottom and darker colors at the top. Tape off and paint the squares, letting each dry before starting the next. To make some squares more transparent, add water to the paint for a watercolour effect.