Hassaikoku no Koukyu Monogatari ~Taikutsu Senkotei to Honsuki Hime~

Princess Suzuka of the Lu Kingdom, a land of ominous colors and the dreaded color black, loves books so much she's known as a “book spirit.”
Years after her engagement was broken off, a chance event leads her to the harem of the Immortal Emperor.
She navigates the treacherous life in the harem using her knowledge from books!