A great choice for buttons, backgrounds and banners, this Rainbow Swirls tutorial can be colourised to create darker, whirlpool-style effects.
Open up a new image in Photoshop, and then click the brush icon in the menu. At the top of your screen, click the little drop down arrow next to an example of a brush and a menu should appear.
Click the brush that says 75, but where it says Master Diameter, change that to 100 instead of 75. Then draw thick lines all over your image in several different rainbow colours.
Go to Filter > Pixelate > Mosaic, and make sure the Cell Size is at 4. Go to Filter > Distort > Wave, and match your settings to the ones below, or similar. After doing this, make sure you don’t have too much of one particular colour on-screen, or your swirl won’t look as good.
Go to Filter > Distort > Polar Coordinates, and select Polar to Rectangular. Then go to Edit > Fade Polar Coordinates, where you need to select 75% opacity and Lighten.
Finally, go to Filter > Distort > Twirl, and choose however much of a swirl you want. I used 999 degrees on mine.