After some extensive Googling I have come to the conclusion that no-one really knows fer shewer, so some informed guesswork is used. Some people have said that a very deep brown (almost black) was achieved using IO's oak, some people say they got black by mixing three other (very expensive) dyes and some people say they probably couldn't have achieved a true black with the dyes at their disposal. Presumably they didn't have gentle washing machine detergents either.
When is black really black? A very dark colour that looks kinda black would be close enough for me.
But they didn't call it black.
So they could have sung 'Blue Moon', meaning a total eclipse presumably ... and 'Don't it Make my Brown Eyes Blue' could have been about getting a thump on the head.
"You're a big man, but you're in bad shape. With me, it's a full time job." – Lt. Bromhead to Prince Dabulamanzi before the Battle of Rorke's Drift.
I'm not sure they can have had a black dyes - I'm extrapolating backwards which is always a bit shaky historically but I'm sure my reading about 17th century uniforms it came up that to dye cloth black they first dyed it dark green (which was expensive enough) and then re-dyed it dark green again. Which suggests to me that true black dyes probably weren't present in Europe before the C17th. I await correction...
It's a question of mass production. The oak apple method was effective but you need a lot of material that is not easy to get. So black was very expensive and very few persons used it for clothes. In Byzantium and other countries they used black to denote high ranking persons . Today we associate paintings of Spanish kings in black robe with darkness and an extreme religious zeal. In fact it was a sign of wealth for the contemporaries.
Oak apple black ink is still produced and used for treaties and similar ritual writings. Today we have other sources for tannin and some other ways to receive black.
The Norrønt languages had some limitations that seemed strange to other peoples. Viking speach was often considered rude by others because they lacked some terms. But there are regional differences. Most saga texts read today are in the old Norwegian and came via Island , so our modern view is a little restricted. Terms for black like blõr and svart are known from other contemporary Scandinavian literature.
Most people do not realize that 'black' is not a naturally occurring color in a nature.
“conscribe te militem in legionibus. pervagare orbem terrarium. inveni terras externas. cognosce miros peregrines. eviscera eos” ̴ “Join the legions, see the world, travel to foreign parts, meet interesting and exotic people, and disembowel them.”