A beautifully blended sample of a carded batt was included in the September Phat Fiber box by After the Sheep. The intense colors of blue jumped out immediately. The fiber content is 70% merino and 30% bamboo--an interesting blend for such a vibrant sample. The bamboo and wool would have needed to be dyed separately. As a cellulose fiber, bamboo requires a fiber-reactive dye and caustic but the protein fibers of wool need acid dyes. Since each process won't dye the opposite fiber, you either end up with something with white streaks in it (because the dye didn't take on one of the fibers) or you do the whole thing twice. Doing them separately means you don't risk damaging the other fiber in an environment it doesn't like.
So I'm guessing that the bamboo and wool were dyed on their own, and then carded together. The bamboo glows with the sheen of silk and really brings out the darker variations in the wool.
I was really looking forward to the yarn this would make until I started spinning. For merino, this batt was a disappointment. There were lots of little bits that didn't want to draft well despite having been carded. There was also evidence of a fair amount of second cuts (little bits of fiber not as long as the rest). These are nice for "art yarn", but when you're trying to spin an even single they make funny little lumps that don't fit in with the rest.
I'm enamored with the colors, but not in love with this blend.