Yuri Project
joined Jul 14, 2016
That probably because it take far less work than inking lot of random background people with dark hair
Exactly my thought. Brown hair needs screentone, black hair needs inking. Generally you can assume that the hair isn't really blond. Just like blue hair or pink hair whatever other crazy colors characters have, if no one comments on it then it's just manga shorthand for dark brown or black.
The "well, that's because I haven't heard your answer" line reminded me of that joke about logicians:
Three logicians walk into a bar. The bartender asks "Does everyone want beer". The first logician says "I don't know," the the second logician says "I don't know", and then the third answers "Yes".