This will add a border to the left of posts and it's done by CSS, in this example i different posts between group types with color:
To achieve this you can do it in the following templates:
Today i will show you the post bit only.
So let's open post_macros and search for:
Replace it with:
Now in Extra.less you need to add the follow, you control the colors per group:
The number identifies the group for anyone that may be confused.

To achieve this you can do it in the following templates:
Code:
conversation_message_macros
post_macros
profile_post_macros
Today i will show you the post bit only.
So let's open post_macros and search for:
HTML:
<div class="message-cell message-cell--user">
Replace it with:
HTML:
<div class="message-cell message-cell--user" id="pstgrp-{$post.User.display_style_group_id}">
Now in Extra.less you need to add the follow, you control the colors per group:
C++:
#pstgrp-2 {border-left: 3px solid #FF0000 !important; }
#pstgrp-3 {border-left: 3px solid #FF4500 !important; }
#pstgrp-4 {border-left: 3px solid #00FF99 !important; }
The number identifies the group for anyone that may be confused.