Subtler gutter

It looks better when the gutter and the code have the same background color, don't you think?

Before:

![Before](http://cl.ly/UEQu/screenshot%202014-03-04%20at%2012.17.28%20PM.png)

After:

![After](http://cl.ly/UFJf/screenshot%202014-03-04%20at%2012.15.16%20PM.png)