Imaginary Girls by Nova Ren Suma
It's been months since I first saw this cover, and still, I'm in awe of it every time I see it. That is like, the prettiest blue I've ever seen. Even though I wasn't too fond of the actual book, I had to feature this cover because it has for a long time been one of my absolute favorites.
(I'm beginning to think I just have a thing underwater photos, right, Mara Dyer?)