generally regarded as positive? no, nor is it generally regarded as negative.
colour? no.
more than one person involved? no.

any person involved? no. (More precisely, it is perhaps possible that people could be involved, or affected, but that is in no way a defining characteristic. I don't think it is a helpful line of enquiry.)

happens/exists/manifests everywhere in world? If it h/e/m anywhere, then I suppose it could h/e/m anywhere, and I suppose it could therefore h/e/m everywhere in the world. Whether it does is quite another matter.

existence independent of human perception? Well, if it has an existence, then that existence is independent of human perception. But it probably doesn't have an existence, in which case its existence is not independent of human perception.

is it fictional? *applause* It exists in fiction. Maybe it also exists in fact. Probably not, though.

philosophers' stone? no.

holy grail? no
single work of fiction? It is strongly associated with a single work of fiction, although it might exist in others that I am unaware of.

da vinci code? no. (you are up late, Chalky...)

[CdM] Yes, I am rather - have been painting and I tend to forget the time. Best be off now :-)

associated with religion? No.
associated with magic? No.
I forgot to mention that the audience applauded Irouléguy's question.

title of a work of fiction? no.

written before 1970? no.
ode to west wind? no.

OK so, to sum up.
We have an abstract something that is associated with, but is not the title of, a single work of fiction written since 1970. It is not associated with magic or religion. It does not necessarily have any actual existence, but if it did it would not be restricted to a single location, nor does it necessarily involve any participation by a person. It is neither a decision nor an event. It is neither positive or negative, nor is it a colour. In addition there are a number of specific things it isn't.
So, it seems to be some sort of concept or idea.

part of a larger work like an aria? It is part of the work of fiction, but not really like an aria.
magic flute? no.
specific work of fiction a book? among other things, yes.
published before 2000? yes.
[INJ] I think your summary is accurate. I go back and forth a bit still on whether it is an event: I suppose it could be an event, although I still feel that no is the best answer to the question.