Button question

normally you rollover a button and the color changes.
I want to make a menu with also rollover buttons (this is not a problem) but this time when i click on them i want them to change like it changes when rollover.
When clicked it should stay that way, till you push in a other button and than that button changes.
It more to show people witch button is active.
Anybody have some coding for it, Tutorial maybe sample files ?