Pixel border between color section and 1/1 block

I am creating a page and the first section has a color section with a diagonal in the bottom.

Next I add a 1/1 box with content in it.

There is a 1 px border showing between them and I am not able to find where it is coming from.

Here is the output:

<div id="after_section_2" class="main_color av_default_container_wrap container_wrap fullsize" style=" ">
<div class="container">
<div class="template-page content  av-content-full alpha units">
Here my content.
</div>
</div><!--end builder template--></div>

And

<div id="after_section_2" class="main_color av_default_container_wrap container_wrap fullsize" style=" ">

Is applying this:

.main_color{border-color: #e1e1e1;}

Where is that coming from?

How to remove it?

I have 2 blocks divided with the diagonal thing, but the pixel in the middle breaks the design.

Thanks.