It wasn't hard to change the background color or replace the header in the CSS:
The little white border around the picture is part of the pic. I just copied the layout's original picture, cut the middle and pasted over my own picture over it. :) [It's just a filler pic, made in a hurry!]
Here's another one for headers without changing the main look of Transmogrified:
And the style I'm using on htbthomas is this (adding the CSS from the above link, changing colors and centering the banner):
EDIT: Make sure to check out dreamwidthlayouts. There are new ones posted all the time, which are really awesome!
LOL, and now I'm using this one! http://sixteen.dreamwidth.org/547.html
Hope this helps some of you out!