JHW Wrote

So in 'Black is the colour of my true love's hair' I will always sing 'his' and think the song has the strength to make it obvious that its words are being sung by a woman even when I (a man) sing it.

I sing "her". I'm not sure that I entirely agree with your assertion here.

While browsing You Tube last night I came across this version by Cara Dillon. She actually sings "her" which I did find strange.