Let's go home, get stoned.... what tool is this?

I think it't the lower slider under the halftone slider...and you flood fill.....that's how I've done this kind of look.

): I like the pretty colors.

I thnk I know how he did this. Slider tool all the way to the right and the pen or airbrush tool at it's smallest and opacity and flow nearly full. Am I right? (probably way off.)