I guess I was fortunate to have English teachers (and others) who taught me to look for meaning in things, symbolism, analogy, metaphor, whatever, but also emphasized that one's interpretation was always subjective. If the curtains being blue means nothing more to you than the curtains being blue, that's a valid interpretation, and it is possible that that's all they are.
Teacher: The curtains were blue isn't just a simple adjective.
Author: Right on.
Teacher: Depression and despair
Author: Wait. I was thinking calming ocean and the character's ability to find his center.
Teacher: You're wrong.
Teachers like that suck. If it's open to interpretation, then it's open to anyone's interpretation, and there's no wrong answer, just the ones you don't agree with.
That said (I know, lots of different sides here), I think that there's times when the symbolism
should be obvious, and if they're dropping like anvils throughout the story and somebody still doesn't see that, then I can understand teachers getting frustrated. In my earlier example (which as far as I know I just pulled out of my ass, although it's possibly a repressed memory or something) where one character's house is decorated in all bright colors, and the other's is all drab, it seems to me that if the author made a point of mentioning all that, then at the very least that says something about the characters. A student could say "Well maybe that's just the colors they like." Sure, but even that says something about them. "No it doesn't. One guy just likes bright colors, and the other likes brown and gray."
Sometimes it's just detail that there's to enrich the story, but not really symbolic of anything. The curtains were blue because it was a bit of detail. And sometimes it does mean something.
I finally read the story of The Astonishing on the band's website, and I think it's great. But as we've seen, it's also entirely possible to just enjoy the music and not have a clue what the story is. And going the other way, it's possible to get
more enjoyment out of it by digging into the story and lyrics and finding deeper meaning in them. That's what art is all about. It means different things to different people, and moves people not just differently, but by differing amounts as well.