The first of these books was published in 1997, and now the material has been updated and made available on a four-hour DVD. It's a very hands-on subject, so it's great to be able to see Ann's demos, covering a wide range of topics.
I found the material to be clearly presented and well-organized. Ann has an "inexact" approach to mixing her dyes. She explains that she is not interested in matching colours, and so she can dispense with exact formulas and mix her dyes instinctively. She achieves many different effects using various techniques, with over 250 samples to prove it.
I learned that there are only fourteen single-chemical dye colours available, and that if you limit yourself to them, you can achieve an infinite number of colours and at the same time gain a better understanding of how the individual pigments behave in unique ways. I also learned that different fabrics accept dye differently and this can lead to very different effects, even when the other variables are unchanged. For example, with a densely-woven cotton, one side of the dyed cloth can look very unlike the other.
Twenty-two pages of notes, intended to support the information presented on the DVD, are available on Johnston's website. .
I would recommend this DVD resource as being every bit as informative as taking a workshop with Ann Johnston, with the added benefit that it's readily available when you need to review the material.