Theme API for NTP search bar, and the about:* pages?

Is there any way to allow a theme to change the colour of the about: pages? All of them are white, and I would quite like to make a dark theme for them.

Also, I noticed that the NTP background and text colour can be themed with the new Theme API, but not the search bar. Is there a property which I can add to my theme so I could change the colour of the NTP search bar?

There’s a tracking bug for allowing such a thing: https://bugzilla.mozilla.org/show_bug.cgi?id=1347201