There is much debate about the colours employed by the Vikings to dye their clothes, particularly as so little survives. What is clear from experimental archaeology however, is that the brightest and the most colourful dyes were usually the most expensive and thereby used by the more well to do Viking. In this category we also find Jet Black and Brilliant White. The former was a mixture of three of the most expensive dyes: cochineal - red, woad - blue, and a brilliant yellow probably weld. The latter was produced by the repetitive process of wetting then sun drying, or else bleaching the material white with wood ash. More mundane shades of grey and very dark brown were commonly worn by the populace, similarly shades of off white were common amongst the lower classes. Earthy shades of brown, pink, yellow, pale blue and brick red were also fairly common. Yellow occurs in many plants and can be quite bright, although some may eventually fade. Wool should always be washed in cool water, to prevent shrinkage, and in any case modern detergents contain optical brightening and bleaching agents, and should be used with care.
All these basic colours are fine for this guide but to help you further, a colour chart of naturally dyed wool using authentic dyes from Sweden is included. (See figure below.)
One final point is that Linen is fairly difficult to dye naturally, and so even a fairly advanced garment may be left undyed, particularly if it is an under garment; for example the Viborg shirt. In the same vein, the York socks were made from undyed wool but decorated at the top with red bands.
This document was taken from Annex 2 titled "Colours" of The Vikings (NFPS) - Equipment Guide No. 1 Basic Costume. It has been editorialized a bit for the WWW.