The iridescence is something magical, a naturally occurring phenomenon in which the wings change color constantly because their many layered semi-transparent surfaces generate multiple reflections in the eyes of a patient observer - sometimes the camera lens, but usually just a faint shimmer.
The physics of the phenomenon are absolutely fascinating, but they are unnecessary here for the moment. The word iridescent comes from the Greek "iris" (or plural "irides") meaning rainbow, and it all begins with the goddess Iris who personified the rainbow on Mount Olympus and acted as a messenger of the gods.
Source: wiccalessons.blogspot.com