From the commissioner:

The third child of Mark Wells and Trixie Lulamoon was their first male foal. The colt was a pegacorn - possessing both wings and horn but not alicorn abilities - but otherwise seemed normal... until they noticed his coat color seemed to be changing. As time passed, it became obvious that not only his coat but also his mane and tail gradually shifted hue through the entire spectrum. When Spotlight grows older, he learns to control his coloration which, if he wasn't a pegacorn, would make it hard to identify him with any consistency until he earns his cutie mark.

The original orange version art is by foxenawolf while the variations were done by me.