The facebook theme is fantastic, as is the Google Inbox theme. The whitelist feature is a little clunky, but it's well worth it for a dark-theme junkie like me.

Miniscule thing: I wish the facebook theme left the facebook messenger custom colors intact. My friends and I color-code our conversations, so I'd like to have that back, but that's an odd use-case, I realize.

Edit: Wow, you took care of that pretty quickly! Thanks guys.