Re: Color
When you change to the Dark theme (via Tools>Options>Appearance>General>Application theme), and hit OK (or Apply) the background/foreground colors will change for everything (toolbars, menus, tool windows, etc.) EXCEPT the editor window(s) (where you edit your source code). The change will be very obvious.
It sounds like you are saying that, after selecting "Dark" for the Application theme, hitting OK/Apply does nothing. I wonder if the option is somehow not "sticking". After you select "Dark" and hit OK, bring up the Options windows again. Does the Application theme still say "Dark" or has it reverted to "System"?