Step 2

You'll notice that I didn't tell you what colour to draw the circle with. Well, that's because it doesn't really matter, the circle we drew is going to be used as an alpha channel, also known as a mask, or frisket. Select Move Layer to Alpha from the Layer menu, and the circle will vanish. Click back to the draw tool , and try drawing on the image with the airbrush. You'll notice that you can now only draw where the circle was. This will come in useful when we colour in the circle, as it prevents paint from spilling where we don't want it. Now clear the paint layer to get rid of any paint you just applied, and we'll get on with colouring in the circle.