This is the velella (Velella Velella), a small free floating hydrozoan. It's currently the only known species in the genus. They're also known as sea-rafts or by-the-wind-sailors, for the obvious reason that it uses the the "sail" you can see in this image for locomotion. Because of this, they are often found washed up on beaches.
Fire rainbows are the rarest of all naturally occurring atmospheric phenomena. For a fire rainbow to occur, cirrus clouds must be 20,000 feet in the air with the precise amount of ice crystals, and the sun must hit the clouds at 58 degrees