TAdvSmoothMegaMenu item color

how assign a different backgrd color for each items ?

Background color can be customized at menu section level:

If you want different background color per item, you would need to create sections with one menu item and set the background color at that level.

As I can see in your image, I assume that you want to change the color of each root menu item.
Unfortunately this is not yet possible, but this would be a great addition to the component.
We will log this as a new feature request.