Added unit test for new theme manager color method.
Added unit test for new theme manager color method.

iOSTestApps/xkcd-Open-Source,IsaacChapman/xkcd-Open-Source,iOSTestApps/xkcd-Open-Source,mamaral/xkcd-Open-Source,IsaacChapman/xkcd-Open-Source,IsaacChapman/xkcd-Open-Source,mamaral/xkcd-Open-Source,mamaral/xkcd-Open-Source