TIme Pass...!!!

A really quick and easy tip for a really nice rainbow like background. And by quick, I mean REALLY quick!
So, let's get started!

Open a new file with about 800x500 and a transparent background.

Go to the infamous Filter/Render/Clouds and then go to Filter/Pixelate/Mezzotint with Long Lines as type.

It looks awfully ugly now, I know.

Go to Filter/Blur/Motion Blur set it to 90 degrees and 999 Distance.
This looks alot better now...

Make a new layer with a gradient from the left to the right, I used Spectrum, but anyting else colourfull looks great.

Set it to overlay and maybe tweak the opacity abit if it doesn't look that good.