Hi @Idan - welcome to our community!  If you’re thinking of the mega-menu itself, the color is defined in the control environment under Customization > Navigation > Background Color. 

As you specifically mention the black bar, however, I think that you want to change the colour of the bar that contains the breadcrumb trail just below the mega menu, is that right?  If so, that color is normally inherited by the the Page Background Color setting available through the Colors settings in Customization mode.  By default, this bar is the same colour as the rest of the page.  If it’s different, as is the case in your screenshot, it was adjusted with a bit of CSS.

I had a little peek at your community to confirm that this is the case - if you have a look in your CSS you’ll find this colour defined as ‘breadcrumb-container’.  You can change the color there or remove that bit of code, after which it will just inherit the page background color.  

Thank you @Kenneth R. It works now! 

That’s great to hear!  I’ll go ahead and mark my earlier reply as the best answer to help anyone else in the future with the same question.  :)