Just draw! Push the up arrow key to change the color a little bit. It'll only change the color a little so you can get different hues. If you hold in the up arrow and draw you will get tye-dye. The down-arrow key will go backwards from the color you're at. Push the left-arrow key to shrink the pen size ad use the right-arrow key to enlarge it. It's at its smallest by default. Push the space bar to change the background. Push the green flag to clear. Enjoy!
Thanks to LiFaytheGoblin for letting me use the pen code! I just changed the stuff I needed to so I could make my own pen game! Update: Music!