Unusual Swallow

Addendum: Apparently, the good birders think this is just a Tree Swallow. It is the brightest blue Tree Swallow I've ever seen with a black and white face pattern I have not noticed before. Gorgeous bird. 

 

 This bird was flying and perched at the far end of our South field this morning when I was closing the horse and dog into that area. All I could see was an intense blue bird acting like a swallow but deep, bright blue. I went back to get my camera and walked, staying out of the bird's view, to where I could get a closer look. It looked like a tree swallow... except it was intense blue with no trace of green... and with a black mask. Is it a color morph of a tree swallow? 

It was all alone. Meanwhile, across the trees and creek in our fields behind the goat barn, scads of violet-green and tree swallows were swooping around as usual, gathering stuff for their gourd nests and eating flying insects. This bird spent most of its time perched on the tall fence around the South field, near the new nest gourds I have put up which the other swallows have ignored... probably because they went up after all the old gourds in the fields behind the barn were already chosen.