Ah, yes. I have the first edition of Sibley's Guide to Birds (poorly printed, virtually everything looks reddish-orange), and had glanced at this page, looking for subadults. I missed this illustration of a variant male adult in breeding plumage, partly because the color is so inaccurate. Note that as I mentioned in my original post, the 5th ed. of Peterson also shows an orange variant adult.
"My" bird, however, was not an adult male in breeding plumage. It was a sub-adult. My Audubon Encyclopedia describes "female, immature, and winter male" as "dull green above, straw-color below, with dark wings and tail..." [p.877], which is what I was accustomed to seeing during my ten years of living in the woods.
As far as I am concerned, this immature bird still presents a conundrum.