PeterLange, I'm a good way into the book and I haven't come accross any mention yet of blue turning purple - but perhaps it may surface later on in the context of something more important - I'll see by the time I'm finished.
.... You sound like a very bright fellow, but there really is no substitute to reading the book before raising issues about whether or not it addresses, confirms or debunks your own particular insights.
1+1= 2, 2+2=4, and changing color saturation on Lab basis is prone to change the perceived hue (see Real World Color Management p.71, or Bruce Lindbloom’s concept for a Uniform Perceptual Lab). Just try said chapter 1 technique to boost both a & b channels simultaneously, and compare HSB hue before / after (in particular relevant for blue to magenta hues).
If the principles of Lab edits are once understood on a 3D basis, it’s hard to call Lab the most powerful color space (anymore). Otherwise, we would have to ask why all other known color gurus did not recognize this, yet.
If Dan’s book only provides a cheerleading perspective on Lab, I’d downgrade it to about point 42 on my reading list. If it also provides a critical review on Lab including strength & weakness analysis, I’d place it among the top ten. Awareness of a problem is the first step to overcome it … imo.
Aren’t we all here to gain (& share) some knowledge and to save some time on this way.