Good questions. The mobile menu will use the colors for the drop-down portion of the navigation menu. It should mirror what’s set there.
The navigation menu is transparent on a page with a hero area. Once the browser has been scrolled down to almost the bottom of the hero section a color is applied to its background like in the demo. There is a color selector that you can use to change the color to something other than black. If you need it to be transparent when it’s scrolled down, you would use this:
Go to the Theme Options page and select the Advanced tab.