What is the difference between a fact and an opinion?

They say you can’t argue with an opinion. This
is true. However, let’s say you are looking at a white wall. You, along with
most people, know that it is white. Then another person comes along and says,
“It’s green!” Then you, knowing the wall really is white, say, “No, it’s
white.” Then the person says to you, “It is green. That’s my opinion and you
can’t argue with it.” And then at that point there’s not much else to say
except, “You may see it that way, but you see the wall really is white. And,
that’s not just my opinion, it’s also a fact.” Granted, most debates are about
things more serious than colors, but my point is: Some things are a matter of
opinion, while other things are facts, whether you want to believe them or not.
What your opinion is, and whether you think it is an opinion or a fact all
depends on you and how you perceive the world around you. Where do you stand? What
is the difference between a fact and an opinion?