How do I remove (get rid of) the grey lines from the middle container?
I have attached a .jpg to show what I am talking about..

Thanks in advance.

That looks to be a border in the top Next/Previous navigation box (ATO>Next/Previous Navigation) and top border for the Post container box (ATO>Style Posts & Pages)

I tried all of the settings and nothing helped..

Notice I have the whole page light blue

The original background is showing through.

These grey lines are in between posts as well.

I remember seeing something #left, #right, no repeat. but for the life of me I cannot find it anymore.

I am back to square one

What version of Atahualpa and WP?
What is the url?

Version: Atahualpa 3.5.3

ato->Style POSTS & PAGES->POST Container