From Wikipedia: Pruinescence, or pruinosity, is a "bloom" caused by pigment on top of an insect's cuticle that covers up the underlying coloration, giving a dusty or frosted appearance.
Pruinescence occurs in many odonates (damselflies and dragonflies). Within the dragonflies it is commonly found in the skimmers (Libellulidae). Typically, only males pruinesce. At least two pruinescent libellulids are found in BC’s Lower Mainland. (Noun, verb & adjective, all in one paragraph.)
Head-on pruinescence: Western Pondhawk, Erythemis collocata, near Chilliwack, BC.
The Western Pondhawk lives around ponds and marshy lakes. The abdomens of females and pre-pruinescent males are green with a dark mid-dorsal stripe. Males eventually turn dusty blue. The generic name, Erythemis, means “the red one.” This is not intentional contrariness; southern species, for which the genus was originally named, turn red.
The Common Whitetail, Libellula lydia. Richmond, BC.
Mature males aggressively defend their territories, alternating between perching on choice landmarks and brief attack-flights at rivals. It is likely that pruinescence acts as a visual territorial threat. It may also help reflect sunlight, useful in a small creature perching at length in the open.