But when I'm in the choir, I'm vested, and so to speak in uniform. Uniforms should be . . . uniform.
Now in our old higher-than-high ECUSA church, the ladies' choir robe included a cute little three-cornered hat. Both men and women wore Elizabethan ruffs. Even the robes had 16th century style sleeves.
If it were an established custom
It was an established custom for women to cover their heads (how they covered them varied by culture or location) when in a church (which includes the choir loft). As with so many other long-held customs, it was tossed when the "spirit" of the council was implemented; ignoring the fact that the council fathers said nothing about changing the custom.
Our choir doesn't have vestments. The men in the schola wear cassock and surplice on the rare occasions when the schola sings in the sanctuary.