Names of living critters are funny things. The more specific they are, the less they seem to correspond to the actual individuals, maybe because life doesn't like being put in boxes.
The Common Whitetail skimmer has a brown or blue abdomen (not tail; that part of the name is wrong, too), depending on its age and sex. It is also known as the long-tailed skimmer, although its abdomen is relatively short, less than the wingspan.
|Common whitetail male, mature. Plathemis lydia|
The young males and the females have brown bodies, with white or yellow side stripes. The mature males are a chalky blue, getting chalkier as they age. In full sunlight, some of them do look almost white, which explains the name.
They catch their food, mosquitoes and other flying insects, by hovering or skimming over the surface of calm water. At least that part of their name fits.