I use the spotlight area. This area have 2 parts:
1) sign up box (in my case log in box) and
2) category posts.
I can choise de colour for the category posts, but can find the place to change the colour of the sign up box. Where I can find the the place where I can put the colour I want?
You can see at: http://www.talkaboutjazz.com. You will see the 1st box (log in) without a background colour and bellow a category post with a background colour.