These sisters (or nuns) took their final vows to be members of the Order which seems to be Benedictine after St. Benedict. This means that their education in the convent is complete and they take a vow, not unlike marriage, to live their lives as poor servants. Sisters are initiated into orders sort of in stages depending on the order and this is the last stage. What I found interesting was as the sisters were lying in supplication, the black cloth that was covering them. I see deaconate and priesthood ordinations every year and they do this, but in the white garment that I think is an alb as the Litany of Saints is prayed. It's unbelievably powerful to see men lying in supplication (face down).
God Bless them, not everyone is called to the religious life.
I may be wrong, but I think that the white veil is an indication that the nun is a novice, and with the final vows the dark veil is substituted/awarded.
Thank you
Actually, in looking again at the photos, I think I am wrong.