Clean code is all about structure. Anything that help show structure, symmetry, hierarchy, or other patterns is bringing your reader one step closer to understanding. The difference between a keyword and an identifier is part of the program's structure. Coloring it makes it visual.
Also, properly-implemented syntax highlighting is essentially a very short feedback loop with the compiler that shows you how your code is actually being parsed. Short feedback loops make creativity easier (this is the basis of a lot of Bret Victor's work).
I agree with the author that "paying attention to what the code is doing instead of the individual elements" is important, but I don't think you have to turn off syntax highlighting to achieve this. At least I don't personally. If the colors are distracting, one idea might be to make them more muted so that they don't demand as much attention. But to me there's no going back from being able to see visually that you forgot to close a string or parenthesis, or include a proper line continuation for your macro.