Ya, short of us having some miracle technology that lets us convert brain waves into video, we will never know what someone really SEES.
But we don't have to do that. The devs and graphic artists just have to mimic what they see in real life.
And we will see it maybe in our own way, and won't be able to tell any difference because whatever way we see things, that's how we always see things in real life. So we will say it's realistic.
Let me make a ridiculous but relevant example.
Imagine the guy making a game sees real life with a red tint on everything. Everything he looks at has a red tone. He makes a game to mimic real life. When making the sky, the guy gives it colour X. He looks at the game, and sees colour X. He looks out the window and sees colour X in the sky. he says the game is realistic.
Now everywhere I look I see green tones. When I buy the game and look at the sky, I see the exact same colour I see when I look at the sky in real life. So I say the game is realistic.
EVEN THOUGH IN OUR MIND THINGS LOOK DIFFERENT, REAL LIFE LOOKS DIFFERENT TOO. So it's useless to even think about that. When you are making a game, or a painting, you don't have to think about how other people will see it.
In both the painting and the game, you just mimic the real life YOU see, and everyone else will see something realistic too.
So it doesn't matter that we can't see through other people's eyes. That doesn't matter when it comes to making realistic games.
Even camera effects, everyone might see those differently. BUT EVERYONE IN THE WORLD THAT HAS SEEN A CAMERA, regardless of how they "see" those effects will recognise that those are camera effects.
So ONCE AGAIN. IF YOU ARE PRETENDING THAT YOUR VIDEO CAME FROM A CAMERA, BUT IT ACTUALLY CAME FROM COMPUTER ANIMATION, USE CAMERA EFFECTS. Example, Avatar movie. highly made in computer animation, adds camera effects to look like a normal movie. But in Avatar, you don't see thorough the eyes of a character, and in games you do.
SO ONCE AGAIN. IF YOU ARE PRETENDING THAT YOUR VIDEO/GAME IS WHAT THE EYES SEE, DON'T USE CAMERA EFFECTS.