Unable to have main menu links change to different color when on target page

I am able to change the mouseover color in advanced styling – but can’t figure out how to have the main menu link that corresponds to the page that i am currently viewing to stay highlighted – a different color from the rest of the links on the menu. I know the original demo had that feature – but somehow I lost it by customizing the colors and the main menu stays all the same color despite which page i am visiting. The only thing that changes is the highlighted line under the menu link.