06:43 in The Secrets of Nature video Sky Hunters, The World of the Dragonfly - The Secrets of Nature the narrator says:
Scientists have been collecting dragonflies since the eighteenth century, but there’s always been a difficulty. Dragonflies quickly become deathly pale, they lose all their color. That’s why collectors have usually preferred to concentrate on butterflies...
and an image of rows and rows of uncolored dragonflies pinned to a display are show.
Question: Why do dragonflies lose all of their coloration once they die?