Changing page colour?

My site is http://empty-purse.com , I’ve chosen this simpsons theme purely for the simple layout but want to change the yellow to this:

url(‘http://i124.photobucket.com/albums/p15/drumbellina/smp6.png’);

EDIT: I’ve figured out the picture, still need help with changing the yellow, thanks in advance!
And I want to get rid of the simpson picture and put my own one there if poss.

Can anyone tell me what code to put where or point me in the right direction please?