Is php5 updated by the web host? If so would this account for the header suddenly stopping working?
Yes, I have come accross this problem as well. I noticed that my blog now only has the default blue header as well. If I try to edit the header image and color via the admin, the upper color and lower color tabs do not work although the font tab still does.
I really need to know how to edit the header colors manually. I used to have a orangy color fading to a sandstone efect and I would like to get it back. Plus I like the idea of having text in the header instead of an image.