Don't know if the following helps, but just looked up the Tanagers in my Sibley's "Bird Life and Behavior" and he says that female Scarlet Tanagers do sing "...particularly while foraging or gathering nest materials. Her song is typically softer and shorter than the male's. The reason for the female's singing is unclear. Researchers speculate that it serves as a way for mated birds to communicate whenthey are separated."
On plumage variations, he has this to say: "Beginning at the end of July or early August, the male Scarlet Tanager molts from his bright red and black alternate plumage to a drab, female-like basic plumage. Individuals show varying degrees of red splotches until molting is complete. Male Western Tanagers (Piranga ludoviciana) also lose some color in winter (most notably their red heads) but otherwise retain the same overall color pattern as they have in summer. Adult males begin to regain their summer colors in March and April. The other North American tanagers do not change plumage seasonally.
"There is some geographic variation in the Summer (Piranga rubra) and Hepatic (P. flava) Tanagers. Western populations of Summer Tanagers are slightly larger and paler compared to eastern birds; western females typically appear grayer above, while some eastern females may show an overall reddish wash. Taxonomists have at times recognized five or more subspecies of Hepatic Tanagers, based on differences in size and intensity of coloration; only two of these subspecies occur in North America."
In my "Birds of Costa Rica" by Stiles & Skutch, the Summer Tanager is described:
"Adult male: below rosy-red; above darker and duskier rose-red; remiges dusky with rose-red edgings. Female: Above olive; below yellow-olive with an overall ochraceous or orange tinge, brightest on crissum. Upper mandible horn-color to yellowish-horn, lower pale yellowish; legs grayish. Immature male: like adult female but below averaging brighter yellow, often tinged with orange and often with scattered red feathers, especially about head, breast, and back. Female: averages duller than adult female, above greener and below more buffy; feathers of wings edged with brownish or grayish."