So what you do is you go to the old editor, and I like to use the biggest size brush but you don't have to, and put two diffrent colors next to each other. I've been experimenting with three color ones, but start with two. You don't have to fill the page, just draw two lines. Then go to settings, and press the red download arrow. Go the the beta editor, and use the blue enlarging tool, and zoom in until it looks like this. You may have to move it around, because you want to keep it centered.

Cool!