Historically progressive compared to its neighbors in the past few decades, huge influx of money and progressive voters recently, all conservative voters have havens in Colorado Springs and some mountain towns so they don’t heavily mobilize in blue areas. CO gets buckets of tourism money, industry (tech, space, research), and likely secondary affects from having a massive airport. Voted in a governor who started and sold tech startups, is gay, and good at moving through legislation.

Prior to California/etc diaspora it was diaspora from the surround states. Wyoming/Kansas/etc all have more conservative values so the progressive young adults often moved to CO.

(Pure speculation)