Why is the new book cover so different from the rest?

Hi everyone,
This is the new book cover to be released in October (well, here in England anyway, the US fecha and cover may be different). All the others have been black, with just a splash of colour for the título and maybe to highlight one other feature (hair, eye colour etc.). I also checked Neferets Curse and that follows the same dark look, why is Hidden so bright?
Thanks xx