Candon Clannach wrote:

Well, we can use Branwen from the Mabonogi as an example.  Her name
means "Blessed Raven/Crow."

in my copy of the Mabinogion and in the already mentioned Lexikon der keltischen Mythologie, too, there's a comment that Branwen is from Bronwen, meaning "white breast". Only because of her connection to Brân  her name got changed.
This translation is really senseful, because white has always been one of the colours of Annwn (by the way, is this connected to dwfn "depth" ?). (In the Mabinogion there are several overnatural animals and persons that are described as white or as white and a bit red, too.)

There are several similar examples among all Europe that parts of the body of  divine beings are white: the Irish Be Find, "Isolde mit der weißen Hand", the cross-crowned stagg of St. Hubert etc.
Especially I want to remember some myths from Central Europe about sea-maids and witches whith unusual large and white (and naked) breasts. (I've read such tales from the Eastern German coast, but also from Thuringia, where once Celts lived.)