Other then the tabs, I prefer a simple blank page without complicated CSS.
One way of doing it is this. Each page has it's own class for the body, e.g.
Each tab should have its own id, tab1, tab2, tab3 etc.
Then put a line like this in your CSS:
You'll have to specify which element of the tab you want to be coloured, I've just put in "color".
Then when the body tab has the class tab3, tab3 will be the selected colour.