How to get a Dark Theme for Android 5.0 (Galaxy S5)

[AC Question]

Is there any way i can change this horrible White only theme that android 5.0 has? everything is white! the settings, the music players, its awfull, looks like iVomit and i cant even change it.. Anything that can help is apreciated, ive already installed theme launchers from google store but i dont like them and they donde acheive what im looking for..

If not possible may i ask then how can i downgrade to kitkat which has a much better looking IMO, Will it run faster or slower than lollipop? and what apps will i miss out if i downgrade from 5.0 to kitkat?

Thanks!