I started this one with a solid purple, then added a lighter purple and yellow with the Rusted Decay brush.
Then I added some orange and darker purple, also with Rusted Decay.
And then used the Flicks brush (under Spraypaints) in orange with reduced opacity.
This one started with a solid medium teal colour, and the Clouds brush with a lighter teal.
Then some medium blue with the Clouds brush.
And just a couple of passes with a darker blue and the Water brush.