I can't understand how a book about design was written by someone who thought it was okay to put black font on a dark teal background... Sure, it's readable to me and probably most people, but kinda hard to see, and I imagine people with certain vision impairments/color blindness or other disabilities that can affect reading would have a harder time. Just grinds my gears how often I see stuff like this, especially when I see it in professional design contexts. This is design 101 people! Form follows function!

it's funny that if they wanted to keep the teal background, white text would have higher contrast (and therefore readability)

Yes! That definitely would have helped, although for body text, even white doesn't show up that great on teal, unfortunately.