Not practical but nice programming
This is a nice little sketch pad here :). Although this concept is unoriginal and used a lot, you've managed to make yours stand out, at least in my view.
Interface is clean and very easy to use, the addition of colors and shape styles are a plus. Nice job on programming here.
Not only that, the graphics are clean, and the drawing is very smooth and clean.
Some things you could add are more shapes and backgrounds. Music would be nice, with mute of course. Some pluses would be the ability to save each drawing.