On white and whiteness

Next post will be the response to this OP.

Madame Y,

Over lunch someone asked me, what is to believe?
I did not know what to answer.
He said: "I can prove to you that ceiling there is not white".
In truth, the ceiling was white.
His proof, the table cloth is even whiter.
This was also true.
I could have said: "Yes that's true, but both are white, and one is more white."
He would have said: "No that's untrue, there is only one color which can be qualified as white."

I was not too tempted to enter into this discussion given his personality.

What is reality? The perception of white?