If you have read my past few posts, you might have already guessed that I will be using conditional codes heavily in this tutorial. Anyway, you actually have different background on different pages. What you need to achieve this? Well, you must at least know how to change your regular main page background using CSS code. You see, there are many page templates and each of them have different ways to address to something, so you must at least do a little homework and try to change it first on the main page.
You can Checkout my test blog for a sample result. Link tab and Contact tab have different backgrounds: