Want something more to think?
Why do we see white or grey? White color is when the value of R, G and B is the same, with grey color is the same.
You can think that the explanation is obvious: white is RGB = 255,255,255 and a shade of grey can be 128,128,128 so it is different.
Ok, now take a better look at the values, the difference between white(255) and grey(128) is the intensity of light, so if the difference is the intensity if we illuminate with more intense light a grey object it will become white.
Let go to practice, look in a room with closed windows, you will see grey objects unless is very dark to see anything, now open all the windows and let the sun light enter, what was a grey object continue to be grey and what was white continue to be white even the illumination in the room increased one hundred times!
Some variable is missing!

And what about the brown color?,  lights that emit brown color do not exist!!!!

Stupidity also evolves!