In the shape of a rainbow

ARCED

Sunlight reflected by airborne water droplets can produce rainbows. The water droplets act as little prisms, dispersing the white light into its constituent colors. Sometimes we see double rainbows. If we look carefully, we can see that the order of the colors in the first and second arcs is reversed.

“Arced” typically refers to something curved or shaped like an arc. In the context of a rainbow, the colors of a rainbow are often seen in an arced or curved pattern in the sky.