Author here! Thanks for the comment. Just for some background info: This book is written for people who want to begin using code as a creative tool, and many readers just learned the basics of JavaScript. Color theory quickly gets extremely hardcore, so the emphasis here is to present an alternative to the standard color spaces that is easy to use in JS. I think that HSLuv solves that problem, and it has been very helpful for my students when I introduced it in undergrad classes. There are many other relevant perceptually uniform color spaces, but none of them are as easy to understand as HSLuv for students who already know sRGB HSL.