I downloaded the new Eclipse Luna (ver. 4.4) and changed to Dark Theme, but the code editor is not changing. See the screen-shot:
I tried this on MAC, Windows and Linux, always the same result.
You can download Eclipse Color Theme plugin as a workaround. It worked fine for me.
After installing Eclipse Color Theme you have to go to: Preferences
-> Appearance
-> Color Theme
, then chose the whatever theme you like, from the screenshot I chose Monokai