I like proposal B (I think it's the most "stylish" one, and adds less visual noise), but I tend to agree with Kevin's comments: I'd like better a mix between B1 and B3: light grey panel + dark grey title. That way, it does provide certain contrast for the title, but doesn't draw too much attention to the panel itself, allowing the user to focus his/her attention on the doc. Otherwise, it does look nice ;)
Greetings, Manuel