Cell Colour Change!!! HELP

I have a cell in my view.php which shows up in all my pages of my site. This is wha tI need to do: If the user is on the home page(index.php) then the cell colour should be blue. If the user is on the compose page(compose.php) then the cell colour should be green If the user in on the registration page then the colour should red and if the user is on the contac us then the color of thecell should be yellow! Can some one point me to an example or provide me with a basic php code structure to work with. Much help would be appriciated! Enrique F.