Rainbows are for My Little Ponies and
Gay Pride parades. If you are uncomfortable with your child being associated with either of these, then don't choose
Rainbow as a first name. She will be teased. It might work as a middle name, though, but only if coupled with a typical first name. I have to second what other people have said -
Rainbow just seems so childish. So if you're young at heart, a hippy, or very open-minded,
Rainbow might work.