Here's a paragraph from an interesting website:
The Icelandic saga literature mentions clothing color. Brightly colored
clothing was a symbol of wealth and power, no doubt due to the additional
expense of the dye stuffs and the multiple dying operations required to make
bright colors. The wearing of black (blár) clothing is a frequent
literary convention in the sagas, indicating that the wearer is about to kill
someone. In modern Icelandic, blár means blue. Presumably, a true
black could not be obtained with dyes of the time, and a dark blue-black was as
close as could be obtained.