A rainbow, for one, is an optical phenomenon that occurs when sunlight is refracted through water droplets in the atmosphere. It is characterized by its seven colors: red, orange, yellow, green, blue, indigo, and violet. The crossword solutions for the term 'rainbow, for one' are 'TROUT' (5 letters) and 'ARC' (3 letters). TROUT are a type of fish that can be found in freshwater streams and rivers, and they are known to be attracted to rainbows. An ARC is a curved line or shape, which is often used to describe the shape of a rainbow.