After visiting the mill and having some students use the Harrisville yarns that come on cones, I do understand her comment in the book (p 28). She says
Harrisville yarns look great on the ball or cone, but the colours grey out when beaten into the tapestry and when combined in the weft bundle. This is probably because they are spun in the grease and are very tweedy looking.Harrisville yarns are spun from dyed fleece. See my lengthy post on my recent visit to the Harrisville spinning mill HERE for photos and more information. The yarn comes to the mill in 500 pound bales of pre-dyed fleece like this:
In this instance, you have to remember your color theory and consider what happens with yarn and color which is very different than paint and color. These yarns are made by mixing pre-dyed fleece. The varied effect in the yarn from doing this is very engaging, but it does affect the vibrancy of the color. If you look at the color cards at the end of the post, you can see that the colors are all somewhat muted. When you mix these already-muted colors of yarn with other already-muted colors of yarn, depending on the hues and values involved, you really can create a very subdued palette. Consider what you want to achieve and choose your yarn accordingly.
I buy Harrisville yarns in white and dye them myself. But at my recent workshop, I was able to try out some of their colors. What struck me was the difference in the feel of the yarn. The fleece has been cleaned when it arrives at the mill and in the picking process (see video HERE), some oil is added back into the yarn to help with the spinning. The yarn is never washed again. So what you get on the cones still contains a fair amount of oil. The yarn is much flatter and doesn't really resemble the fluffy, beautiful yarn that I use (which does, after all, come from the same mill). If I was going to use their colors, I would skein the yarn and wash it before I put it in a tapestry. This would restore the loft and it would also mean that your finished tapestry didn't have that oil in it which may be an attractant to bugs. Harrisville Designs actually recommends washing your piece after weaving to restore the yarn's loft. Of course they are assuming you are weaving cloth and not tapestry. You would never wash a tapestry in the washing machine or even bathtub, right?
Another option is to buy the yarn in the 3.5 ounce skeins that are sold as knitting yarn. This yarn has been washed and has much more loft right out of the box. I often buy this skeined yarn in white and dye it myself, but I find that I still need to scour it one more time before dyeing or the dye doesn't take evenly.
Harrisville yarns come in 64 colors. The color range is not designed for tapestry and doesn't have much in the way of color gradation. But the colors they do have wove up beautifully. No they are not bright jewel-tone colors, but they are lovely. For example, this student sample was woven completely with Harrisville yarns straight from the cone.