This is great! Had fun playing with it for 10 minutes. A UI note: a common behavior in pixel-based editors like this one is: When you click on a blank pixel, f

This is great! Had fun playing with it for 10 minutes. A UI note: a common behavior in pixel-based editors like this one is: When you click on a blank pixel, fill it with color. As long as the mouse is held down, you're "drawing" and moving it to other blank pixels should color them as well. Likewise, when you click on a colored pixel, erase it and stay in "erase" mode as long as the mouse button is held down. Saves a lot of clicking, I think!