To aply a backgroud color in a Mega Menu submenu You have to modify the file mega.css
Folder : templates > ja_purity_ii > css > menu > mega.css
.ja-megamenu li.mega .childcontent { display: block; height: auto; position: absolute; background: #000; }
In the example, I chose a black background (#000000).
This operation will change the background color for all the submenu. For changing it in columns , we will change another CSS class.
