How to detect if OS X is in dark mode?

Question

Don’t think there’s a cocoa way of detecting it yet, however you can use defaults read to check whether or not OSX is in dark mode.

defaults read -g AppleInterfaceStyle

Either returns Dark (dark mode) or returns domain pair does not exist.

EDIT:

As Ken Thomases said you can access .GlobalPreferences via NSUserDefaults, so

NSString *osxMode = [[NSUserDefaults standardUserDefaults] stringForKey:@"AppleInterfaceStyle"];

If osxMode is nil then it isn’t in dark mode, but if osxMode is @"Dark" then it is in dark mode.