I want to say yes because apples are indeed yellow but not ALL apples are yellow. So where does this statement fall in terms of objectivity and subjectivity?
I think we'd call things like that poorly formed instead -- it could mean more than one thing. The confusion is that in normal English most seemingly ambiguous statements mean one specific thing from context. For example, "people can hold their breathe for 10 minutes" obviously means there exists at least one person who can do that. Whereas "that can't be a dog, dogs don't have scales" means that all dogs lack scales. "Apples are yellow" would be understood to mean that if you go to stores with a medium selection of apples, at least one type will be yellow. It's not partly true -- the thing we understand you're really asking is completely true.
For something where we can't guess the intended meaning out of all likely interpretations, like "medieval peasants could read", calling it partly true just isn't helpful. It merely means that at least one peasant in the half-century of peasants could read, while at least one couldn't. I mean, "apples are polka-dotted" is partly true if I think you're asking whether apples can be painted. So I shouldn't say that, I should ask for clarification instead.