rainbow tunnel

The trick is really simple, first you just draw rings around the center of the page, and tweak their position a bit depending on the position of the mouse.

To achieve the rainbow effect, you just have to make it so each ring has its hue value a little higher than the ring before it, and increase all of the rings' hues each frame.

I did it a little different than that, I have a base hue, which I increase every frame, and then when each ring gets drawn, it uses the base hue plus a small increment (which you can control with the mouse wheel).