Delphinian was coined by Tumblr user Genderless-Gibberish on July 9, 2018. The term comes from the delphinium flower.
The flag was designed by Tumblr user Nooonbinaryyyy on July 9, 2018. The first three stripes come from the colors of the thistle flower. The white stripe represents the absence of gender. The green comes from the agender flag.