The line above the signature? Or the Bar Above the post that has todays date and post number on it?
The gray bar is to separate post content from signatures... You've seen sites where the break isn't clear and you're 5 words into the signature before you realize you've read that 1,000 times before.
The Blue Bar is to separate and define individual posts. Those do need to be dark as they are the horizontal separators when scrolling. The eye sees it as posts, instead of a long sheet of flat info with a bunch of posts somewhere in there.
We can change the color of each, but they need to remain dark, and in the same color spectrum as the rest of the forum.
Nope. Look at the grey bar running under Wayne's FAFD link, in between there at the "Edit Post/Reply" line. It's a faint grey line and that has been on several posts. I like the new solid grey line to break things up, but this is same color as the grey around the avatars. It happens to not appear in your post though...