I think they would try to convert them so they could be saved!!
Genesis 9:16-17
16 When the rainbow is in the cloud and I see it, I will remember the everlasting covenant between God and every living creature of every kind on the earth.
17 So God said to Noah, "This is the sign of the covenant that I established between me and all life on earth."
and - I thought Rainbows were naturally occuring by the refraction of light through waterdroplets.