I am taking a series of workshops on Cape Cod with a wonderful instructor, Kate Aubrey. The most recent workshop focused on trees, outer shapes, bird holes, and values. Kate asked us to focus on lights, mediums and darks using one color. I selected French Ultramarine. Kate suggested working from light to dark, which worked well for me. Another interesting source, for newbies to watercolor like me, are books by Steve Quillar that focus on value and mixing colors. I think I may buy the Quillar Wheel, a map of how to mix colors. It’s also in most of his books and/or it is sold on Amazon.