Fengender is a xenogender exclusive to Chinese people and is used to describe a gender that is like the wind; playful, fickle, and all over the place.
This term was coined by an anonymous Tumblr user on February 23rd, 2017. 
The flag was designed by Tumblr user ask-pride-color-schemes and the anonymous user who coined the term on February 23rd, 2017.
The designer picked the blue-purple color since it’s an ambiguous color (represent nonbinary) and its a nontraditional color for an element. The classic Chinese elements are fire, earth, wood, metal, and water. The colors for these are traditionally red, yellow, green, white, and black respectively. Hence, wind/air isn't considered one of the elements in Chinese culture, and blue and purple aren't used as traditional colors.