Blue Roses

Blue roses do not exist in nature. In 2004, researchers used genetic modification to create blue pigmented roses. This item is dominant in both the Blood+ anime and manga.

In the Anime
Blue Roses are flowers that are part of a legend called "Legend of the Phantom." This legend was told to Saya by her roomate, Min when Saya is given the assignment to infiltrate a Vietnamese boarding school, Lycee de Cinq Fleches ("School of Five Arrows" in English). Blue roses are only found at a rose garden next to the church at the school which is off limits too the students. Ms. Lee won't let anyone go near the garden saying it's dangerous. Rumors evolve around the garden that the blue roses bloom there even if there's no one taking care of them. There is only one place where Saya could see the rose garden from and it is the bell tower. So after dark Saya heads to the garden with Hagi, and find blue roses growing around the entrance to an underground area. Once they go below the garden, they find that the door to the rest of the area is locked but Saya does see a container with the number 721226 on it.

In Manga
In the Blood+ manga, blue roses are shown to be found at only one place, a village in Vietnam. It grows all around Charles' mansion. It was also a common favorite of both Saya and Diva before the Bordeaux massacre.

Trivia

 * Blue roses are Diva's favorite color roses. They grew all over the outside and inside of the tower in the zoo where she was locked up.
 * Three of the clothes that Diva wears in the series, have a blue rose on it.
 * Saya receives blue rose three times in the series: two from the Phantom (on the bell tower and in the classroom) and one from Solomon during the ball where he puts it in her hair after their dance.
 * Blue roses are often portrayed in literature and art as a symbol of love and prosperity to those who seek it.