The program lets you draw single points and single pixel width lines. There's plenty of features that could be added, like different line widths, brushes, airbrushing, erasing, and so on.
One of the challenges is that the screens are small and adding a tool palette will take up more of it. Using a popup palette will make better use of screen space. Button B could be used to open the palette, or touching in one corner of the touchscreen. That would provide plenty of room for color, tool, and brush selection without using up canvas space.
Another enhancement is to add a Poller class specific to the joystick on the PyGamer. This could provide more granular direction control or absolute positioning (the cursor location would correspond to the joystick position).