We've all seen them before. A rainbow is an arc of light separated into bands of color (parallel stripes) that appear when the Sun's rays are refracted and reflected by drops of mist or rain. The colors of the rainbow are red, orange, yellow, green, blue, indigo, and violet. These are the full spectrum of colors that make up the sun's white light. They can also be created artificially, using a prism.
Enter your most artistic photo of a rainbow or rainbows. They must be REAL rainbows! Pictures of rainbow flags, clothes, etc. are off theme, however prisms or other objects that split light, are not. If you can stage it, do it! Anything goes so long as the rainbow is the main focus.
To get some real "rainbow inspiration" make sure to check out the double rainbow guy
Have fun and good luck.