wow, this thread is really interesting. thanks for all the responses from a mostly silent reader of this list :-)
 
some minor comments: to the gaeilge / gĂ idhlig question: yes, the words for colours are the same in irish and scottish gaelic, the languages are close enough for that. by the way it is a common thing that different languages use different divisions of the colour spectrum. it is not, that they "use the same word for two or more different colours" - that's just how it appears from the perspective of another language with a different perception. in gaelic there are words like "gorm", "glas", "liath" and "dubh" to cover the broad range of blue, green, grey and black shades which are manifold in nature. the differences between the words are not easy to explain by translating, because the perception and division of the colour spectrum in english is different. i only learned it when gaelic native speakers gave me examples, like what would you say to this colour of grass or that colour of the sea or the sky on a certain day, and so on.
 
another question mentioned was the possibility of dying real black clothes in medieval times. i remember a similar discussion about that in a medieval forum for experimental archaeology, and most of the people there agreed that black was a really rare colour, it is not possible to be dyed with early medieval methods, and later, when it became more possible, it became the colour of clerical people and was usually not worn by others (but this is a matter of dress codes which only developed during the middle ages and were not fully existent in early medieval times).
in that forum they also discussed the possible existence of sheep with black wool, and if i remember it right, it was unsure whether such races of sheep existed in northern europe in early medieval time. i think they agreed at least on the existence of dark grey and dark brown :-)
 
just my two shillings to the discussion :-)
mona