JUST come up with this concept now

How would I be able to do it so; every time the website refreshes it loads up a new .css file.

For instance, someone goes to "the site" and they'll see a blue layout because it's loaded up the blue.css file. But then the user refreshes and it loads up the pink layout because it loaded up the pink.css file etc etc.

For say a maximum of 10 css files or however many css files are in the css/ directory.

Anyone got any ideas, links to help, or help themselves?