Is there a default "dark" theme (i.e. black background)? For the majority of its life Android has had a dark UI (color text on black background), then it switched to light background on Android 6.

Android 7 will feature a "night mode" which will permit to restore the black background, having the standard UI in reverse colors.

While waiting for it, is there a "dark" theme for Android 6 that would have the same effect?
Apparently the "night mode" promised for Android 7 hasn't been implemented after all, but there's a High Contrast Theme by Samsung for Android 7 that works in a similar way.