The main yarn for my Taiga sweater is Briggs & Little Heritage in Sheep's Grey. From what I understand this is an undyed colour - the natural colour of the sheep's wool. And a very traditional colour for a sweater.
At the mill I learned that traditional fisherman's sweaters were knit from undyed wool. By leaving some of the naturally occurring lanolin in the wool, the resulting sweaters were somewhat water repellant - handy for keeping a fisherman warm and dry. But Lanolin (L. lana "wool" + oleum "oil" + chemical suffix -in.) is a waxy substance which resists dyes - hence the yarns were left undyed.
There's something very comforting about tradition. The colourway is very muted and comforting - although in this wool the lanolin has been washed out with detergents. It's a bit closer to nature without harsh chemical scouring and inorganic chemical dying. And it smells very woolly.