I want to change the menu color in premiere pro cc 2018 from white to black so that it matches the inner interface.
The answer to your question lies here. You may not be able to change the appearance to the point where is also affects scroll bars, title bars and menus that aren't inside panels. I have highlighted the related section of text in that link below:
Brighten or darken the interface You can lower the brightness, as when working in a darkened editing suite or when making color corrections. Changing the brightness affects panels, windows, and dialog boxes but does not affect scroll bars, title bars, and menus that aren’t inside panels. In addition, the change doesn’t affect the application background on Windows.
Choose Edit > Preferences > Appearance (Windows) or Premiere Pro > Preferences > Appearance (Mac OS). Drag the User Interface Brightness slider to the left or right. Click Default to restore the default brightness level.