At the front of the eye is the cornea.  It is a very important part of the eye because it keeps the eye focus. It is clear and transparent. Behind this is colored ring Iris, with a hole in the center, the pupil. The pupil is black in color and it lets lights enter the eye. Behind the pupil is the lens, which bends the light rays. Light rays pass through the cornea, pupil and lens into the interior of eye. A sensory nerve called the optic nerve joins the eye to the brain.

Retina contains 137 million small cells, which can react to light. Most of them are rod-shaped and some of them are cone-shaped. The rods are responsible for black and white vision and the cones for color vision. In dim light, activity of cones diminishes and so everything looks gray.

Eye has millions of electrical  connections. It can easily receive 5 million messages at one time. In bright light pupil is nearly closed, on a dark night it is wide open.

When we see things with eyes, we actually see them in our brain. The bright light passes through lens and falls on the retina. Immediately a tiny wisp of electricity is produced. This passes to brain through optic nerve at a speed of 500kmph. The brain receives the signal and understands it (then we feel we have seen something). All this happens in 0.002seconds.

We see with our eyes and brain. But our eyes capacity to see is very limited. It can neither see very distant objects nor very small objects clearly. To see very small objects like bacteria, plant and animal cells, blood corpuscles etc., we use a microscope. In order to observe distant object like stars, planets, satellite etc., we use telescopes.

When there is this (seeming) duality, then only one sees another. This refers to the process of human perception. Our perception is based on the duality of subject-object relationship. For example, when one sees a table, eye is the subject and table is the object. The eye see the table- the object- because our powers of Vision are finite or limited and our vision stops at or is obstructed by the table. If the power of our vision were infinite, then it would have gone through the table and everything beyond and ultimately returned to the eye. What is true of perception, is also true of all other sensory knowledge of hearing, touch and smell. There needs to be duality or two factors. Our life is so organized that we can function only with finite or limited powers. We are given powers that help us do a few things but they also act as delimiting factors.

We see sunshine dazzling our eye on the earth but when astronauts go into outer space, although a million sun like stars throng the heavens, they find the space dark. The reason is that one can see light only when it is reflected by particles (which we have in plenty in the earth's atmosphere) but the outer space is a vacuum with no particle, which can reflect light and make it visible.

We see different color because, each object observes a specific light and reflect a light of a specific color. This is how we see different colors.