Understanding oxidized output

Hi guys … my oxidized platform is working ok.
I just need a little help understanding what im seeing here.
I already tryed with diff tutorials but can get what is going on on my router configs.
When clicking on version diff buton it is placed at right of screen.
Then you can choose on the left against witch version you want to compare.
Question is …
Placing latest version at the right and and previous on the left , what does mean:
a_ colors (green , yellow and red).
b_ simbols: @@ -103,15 +112,6 @@.
c_ diff --git a/x.x.x.x b/x.x.x.x

I did not write the router config, just trying to understand what router admin did using diff analisis.

Any help would be pretiated.