Michael,

The setting for this is in the menu.css file which can be found in the following directory: Portals/_default/Skins/MinimalExtropy/css. The red is created by a tiled background image, which you'll either need to replace or remove and adjust the CSS to show your own images or colour.

Another option to change this is to add the new css to the CSS Editor which can be found; admin > Site Settings, the CSS selector for this is:

.mainMenu .sel, .mainMenu .bc{
put your CSS in here
}

Regards,

Rick.