The fact of the matter is the general color tone is described as red, but what if someone is color blind, and cannot see red, or their ocular nerves work differently and they see red as lighter or darker. You cannot actually say that the same two shades of red will look completely the same to two people, but you have a general idea that it is red.
Perceptions between people can differ on a variety of things, both subjective opinions and what we think of as objective reality. Variations in physiology can cause people to have different experiences of the world around them. Just as some people have different abilities to see clearly from different distances, people can see variations in color, even if the person is not color blind. When one person says something is a certain color, another person may not see it that way.