I never realized how many people couldn't tell the difference between an opinion and a fact.
Opinions vary from person to person. Even if it is a consensus, it's probably still an opinion because it can't be proven. It can be proven that there is a consensus, but that only makes the consensus fact, not factual. The consensus exists, but what it pertains to isn't necessarily a fact.
Facts can be proven. Opinions cannot be proven.
Is Paul Walker a good actor? That depends on whom you're asking. Thus, any answer would be an opinion.
Do humans need air to live? Yes, and that is a fact. It doesn't matter who you ask; everyone who lives, breathes.
Is the sky blue? This is a tricky one. It's an opinion. Why? Because you can actually get different answers for this one. Someone could easily say the sky is light-blue or periwinkle. Blue is a relative term, because so many people have broader and narrower opinions on which colors they consider "blue." Just go to a hardware store with someone of the opposite sex, look at a color palette, and see how many colors you both name differently.