That one leaped out at me too. I don't believe the author is cheating though, he just hasn't fully explained what he did in the step. From what I can deduce,

That one leaped out at me too. I don't believe the author is cheating though, he just hasn't fully explained what he did in the step. From what I can deduce, and my own experience, he more accurately means: "one [slightly] darker color [and one slightly lighter color]", "add shadows [and highlights] where needed", and "repeat with progressively darker and lighter colours at deeper shadows and higher highlights until you are happy".