Change button's colour

I need some help!!!

I will like to change the colour of my navigation button’s when you click them.
So when you are in a section that button will be on a different colour (people will know on which sections they are). The buttons are plain text only.
you can see an example on this site: http://flash.perfectusds.com/chrisalanwilton/portfolio.html

thanks in advance

nekoweb