Shades of Magic (3 book series) by V. E. Schwab (Author)

A Darker Shade of Magic, from #1 New York Times bestselling author V.E. Schwab

Kell is one of the last Antari—magicians with a rare, coveted ability to travel between parallel Londons; Red, Grey, White, and, once upon a time, Black.

Kell was raised in Arnes—Red London—and officially serves the Maresh Empire as an ambassador, traveling between the frequent bloody regime changes in White London and the court of George III in the dullest of Londons, the one without any magic left to see.