After you finish the value drawings - maybe after Tuesday's class start in on some water color still lives. <-
Look on my documents page and do some water colors... They needed be apples - find some things you'd like to paint. Apples, fruit, or anything living is good because they have depth of surface - the light is reflected off the apple's skin which has depth and transparency to it. Watercolor at it's best hast depth and transparency to it - that's the point!