The yarn I am using for this first project came from 100 percent pure wool. That link takes you to the exact skein I'm using. Here's one of their product pictures, which captures the amount of variegation in the skein. The color in this is a bit warmer than the skein I purchased.
The color as it came through to my house is more blue than the picture above shows. It's almost a greyish purple, but variegated as shown in the pictures.
Working with this yarn, it is exactly as described. It is a yarn single, which doesn't bother me as far as knitting it up. Some people prefer a more balanced yarn, but in an organic pattern the twist of a single can be quite charming.
The only issue I have with this yarn is that it is not a consistent spin. This means there are some areas in the yarn which end up thick, and others which end up thin. It's not a traditional thick and thin, and I know it will be quite stable and sturdy when knit up. I have worked with this brand of yarn in the past, and do not find it to be at all weak, even though it has some thinner spots.
However, someone who prefers more consistency in yarn thickness would want to choose a 2 ply instead of this single. Singles that are a bit more consistent can be found in Schaefer Yarns, and I've had good luck with Handmaiden yarns for their singles consistency as well.
This single with it's inconsistency is perfect for this pattern, I think. It adds a realness to the organic flow of the pattern, without losing anything in it's strength or beauty.
I do recommend both this yarn and this company.