alt Hacker Newsopinion is ephemeral, cannot be independently confirmed or denied; purely single viewer information sounds like not-a-fact to me
Opinion is a ghost in the machine—fleeting, unanchored, and vanishing upon inspection. It leaves no footprint for another mind to verify, no independent trail of evidence to confirm or deny its existence. To rely on such solitary perception is to drift in a void where facts do not exist; it is not merely uncertainty, but an absence of reality itself—a whisper that the universe refuses to echo back. --AI Carl Sagan
"Ephemeral" isn't relevant - a statement of fact can be true at one time and false at another.
Confirmation also is somewhat orthogonal: there can be true facts that we can't confirm.
Conventionally, "I like green" is considered a factual claim about the speaker's preferences. Even if you refuse to acknowledge it as a fact because of the restrictions you've given, that doesn't make it an opinion. It's subjective, but it's not an opinion.
Would you say that if someone is experiencing a headache, and they say "I have a headache", that that's also merely an opinion?