Quote - 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.

 
Human vision is also highly influenced by edge effects, and boundries between blocks of color. I saw a wonderful lecture given by Dr. Land where he projected a bright circular spot light on a board and asked what color the object was. The audience all answered "white". He then removed the mask from the spot and, with the same lighting over the whole board, we saw that the light had been illuminating a red circle on a board with various colored polka-dots.