Here is a loadable background you can use in an OS, for example. Normally it takes around a minute, turbo mode is a few seconds. (shift-click) for turbo mode. To make a new colour, just pick two colours and fill in a shape with the the fading up-down effect.
I was just messing about and I made this... hmm. Kinda relaxing tho. Please give me credit if you use it!