Who was the Goddess of the rainbow

Iris
In Greek mythology, Iris (/ˈaɪrᵻs/; Greek: Ἶρις) is the personification of the rainbow and messenger of the gods.

She is also known as one of the goddesses of the sea and the sky.

Iris links the gods to humanity. She travels with the speed of wind from one end of the world to the other, and into the depths of the sea and the underworld.

Read more...https://en.wikipedia.org/wiki/Iris_(mythology)