Sidebar background colour change between pages -- possible?

Hello Atahualpa folks,

Up to my eyeballs in new site stuff... and was wondering if this were at all possible: Can you have a sidebar background colour change depending on which page a user was viewing?

Here's the site (work-in-progress!) in question.

Here's what the designer wants to happen. (PDF)

In the PDF, see how the right sidebar background changes colour depending on which page is being viewed (colour corresponds to the pages on the left sidebar)? Is this doable? If so, any advice or hints on how I should go about it would be invaluable!

Cheers,
Misa