Remove Wrapper color

Hello, I have a new website at this temp address: http://mistermallow.netfirms.com/patmos/ If I have the background color the same as the header color, I see a 1 pixel line around the header block. I searched the CSS for a "wrapper" or something that caused this line but I could not find it. You can see at the image here where the line is: https://drive.google.com/file/d/0B4F90kSrLIxhb3Vnd3k0QkR3UDQ/view?usp=sharing How can I remove this line? Thank you for your assistance.