Rainbow is a fanmade Sing-a-ma-jig by Garrettnix555. She is rainbow colored, her ears are very thin, she has pink heart eyes, a mint green nose, a light blue mouth, a green vertical striped shirt and she sings "Somewhere Over The Rainbow". She has the same voice, pose of arms and shape of feet as the Valentine's Day Sing-a-ma-jig.
Rainbow sing a ma jig

This is what she would look like.

She signs on, enters song mode, and signs off the same way as the Valentine's Day Sing-a-ma-jig.