Hi Raffi. I can understand why you would want this, but unfortunately X3 skins are created with a lot of inheritance complexity. Changing the topbar background color would affect font colors + hover, background colors + hover, dropdown menu and mega menu (and all links and items within), as well as the topbar FIXED colors (when topbar is fixed and/or overlaying an intro video/image/slideshow).
Sounds like perhaps you have touched upon Boostrap earlier since you use the term "navbar"? Yes, then it would be simpler if you were building your own html structure and could choose different navbars separately from the website's own style. In X3, we need to use one style to adjust colors for everything on the page. Perhaps this can be improved in the future, especially since we intend to migrate to Bootstrap at some point.
Until then, you can only edit the topbar/navbar by adding custom CSS (Settings > Custom > Custom CSS). Keep in mind, once you edit the topbar background color, you may need to adjust styles for lots of elements that display within the topbar under various circumstances (snowball effect).