Disclaimer: Do not use in production. Nothing of this works in Chrome (because they have not uprefixed gradients, just yet)
Pure CSS Triangle: http://jsfiddle.net/GBjXp/
Boring, just another triangle.
Simple color mix: http://jsfiddle.net/ugPUu/
Boring, RGB colors @ 120 degree shift.
Eye in a Tube: http://jsfiddle.net/qAYbK/
Overlaying radial gradients.
Notice how Firefox is starting to experience troubles with this one - dirty colors, stuttering. Special: drag/resize jsfiddle's layout grid, and you will see how Firefox draws radial-gradient all over your screen.
Liquid sky: http://jsfiddle.net/8Q8dj/
Something more visually enoyable.
This one is using background-size to patternize gradient, small alpha hsla for spiral gradient, also, corners are bluntly hacked.
Looks as intended in ie10/o12, but FF19 adds extra psychedelic effects, which you might decide to enjoy