Well, I learned in Science Class that your brain is used to the color, which the only way to see the color, is how the light reflects on it. If you try an experiment, like this.
Put on a shirt, (Black is good) with some lettering. (white is good too!)
Look in the mirror, and turn off the lights. After a few seconds, the light comes back becasue your brain is telling you that it is that color. Weird huh??
grey
Green.
red
A whitish grey colour.
the colour for traumatic brain injury is green.
get a brain
not as colorful as my brain
greyish pink I would suspect
The largest proportion of the brain is grey in colour. So when someone says this they mean use your brain or think.
Our eyes are our sense organ for detecting light. Their colour range is somewhat limited, being about one half of an octave. When we say we 'see something', or 'are looking at something', in reality we are merely receiving light from that object. We use separate sensors for brightness, and for colour. For colour we have three different colour sensors, which overlap in their bandwidth. Thus we perceive a broad range of colour. In dim light, our colour sensors are not active. Your eyes are an extension of your brain (whose whole surface is light sensitive), and each eye sends part of its output to both hemispheres of the brain. Many herbivores and carnivores have little use for colour, and waste no brain power on it. Some insects and butterflies can see a much wider range of colours that humans do.
Normally, this is inherited, but if it is not, then considerable damage to the Optic Nerve, Retina, or higher brain can cause this.
The color you see when your eyes are open are a function of your brain interpreting light rays. When you sleep your brain can play them back to you. You don't see dreams with your eyes, but in your mind.