Any color of oleander flower is poisonous, as all parts of this plant are poisonous. This does not mean you would die if you were to eat it. The toxic dose varies with the individual, the plant and with how much is eaten.
If you are trying to avoid poisonous flowers, stay away from the white oleander. They have toxic compounds which can be deadly and especially can affect young children. They are being promoted as healthy without any proven benefits.
White oleander flowers are poisonous if ingested. There is actually a book titled "White Oleander," by Janet Fitch, which describes the protagonist murdering her ex-boyfriend by dissolving the flower in his drink.
