Button question

Ok so i have made a number of buttons.

What i would like to know how to do is make it so that you see what buttons you have pressed.

For example after the buttons has been pressed it turns red, and stays that way until the site is reloaded. i have seen this on a number of sites, just cant figure out how to get it to work myself.

The attached fla is an example, Now how could i make it so that once the button is pressed, it will turn the color red and stay that way?