Thank you to all that replied with help (direct and through the listaserve)!
I have to admit to being one of the ones that quickly sift through an area relying heavily on my ears to pick up a "different than normal" chip note or partial call and don't take much time to physically view and optically "study" the birds as well as I should. I'm fortunate that this swallows lackadaisical behavior was such that it made me look twice and even a thrid time.
It seems that more times than not, my swallow observations seem to take place with them either on a wire overhead with backlight or while in their somewhat erratic flight - seemingly never while standing over them at 9 feet. It was a great opportunity to remind me to slow down and take that second and third look (if offered)!
Despite hoping for some amazingly wayward swallow, I decided not to hold my breath until I knew that it wasn't a regularly encountered swallow. My initial thought was, "Could this be a Violet-green?" After reading the link that June Newman sent and then looking up in my Sibley's Guide, I feel confident that what I was watching was, in fact, a Tree Swallow, in what is described as post juvenile molt. See below:
A complete postjuvenal molt takes place, beginning late in August and continuing into October. This produces a first winter plumage, which is practically indistinguishable from the winter plumage of the adult. Dr. Dwight (1900) says of this plumage: "Above iridescent green, sometimes with steely blue reflections. Wings and tail deep bottle-green slightly iridescent, the tertiaries broadly tipped with white. Below, pure white slightly smoky gray on the sides." The white tips on the tertials are characteristic of the winter plumages of both adults and young birds; but these tips wear away before spring. There appears to be no spring molt, but a complete postnuptial molt begins about the middle of August and is usually completed before the birds go south. This is the only one of our swallows that completes its molt before migrating; it breeds early, molts early, and migrates late.
Link that June Newman provided (for reference): http://www.birdsbybent.com/ch81-90/treeswallow.html Thank you June. This was the last nail in the coffin for me as to the I.D. As June stated in a previous response, the Violet-green has facial coloring where there's white showing above (around) the eye, whereas the Tree Swallow has a distinct horisontal line of color versus white that runs below the eye (as shown in the individual that I observed/imaged).