Each object has three basic qualities that define it: size, shape and colour. Our brain tends to think that the nature of the colour of each object is the same as the other two qualities. A priori, colour is something that exists, it is something that we see and can define and touch: the colour of a cup, the colour of a logo, the colour of a t-shirt exist. However, this is not the case. It is an illusion, a “sensory impression” made by our eye, the product of the activity of contemplating a material or object, which is affecting the perception system of human beings, or in other words, how we perceive.
“Knowledge of the basic laws of colour theory should be an integral part of general education. (...) Not only is it lacking in the curricula of primary and secondary schools, but it is rarely found in the curricula of higher and vocational schools.”
Harald Küppers (1921 - 2021)
Our vision, always subjective
The working principle of the organ of sight explains, and therefore gives rise to, the theory of colours. If we understand how our eyes work, we understand why we perceive colours the way we do.
The visible spectrum of the human being only covers a small part of the entire electromagnetic spectrum. The different colours perceived are due to the fact that each object or material has specific absorption characteristics of different visible wavelengths. The colour that results in each object corresponds exactly to the wavelengths that the body or the matter that composes it is not capable of absorbing.
These waves, which are not absorbed or passed through by the body or object, bounce back and hit the human eye, and are processed by the brain as colour. In this sense, colour is not a phenomenon in itself, but rather a 'colour sensation': a perception of sight. In the case of transparent materials or objects, these have the quality of absorbing the entire spectrum of light perceptible to the human eye, and that is why it can see through them: they have the quality of letting all incident light pass through.
The law of vision and the different types of objects - in their opaque, transparent or translucent condition - constitute what is the fundamental theory of colours. Objects of a single colour cannot be defined as homogeneous objects. Each and every one of them has a "body colour", conditioned by the existing lighting. Therefore, if you have ever been in a group of friends debating the colour of something that you all have in front of you, it is possible that you have all perceived a different colour or shade.
If light is understood as "quanta", the number of tones is infinite, and therefore a body can have infinite shades of color, which humans try to define through language.
How the human eye works
Light rays pass through the surface of the eye, reaching the retina, where the photosensitive cells called rods and cones are located at the back of the eyeball.
The eye has the ability to automatically adapt to different levels of illumination, that is, it adapts to the differences in contemplation that stimulate it at any given moment. These changes can be qualitative and quantitative, and correspond to the work carried out by the two types of cells mentioned above.
What are quantitative and qualitative adaptation of the eye?
The human eye sends a series of signals to the brain that affect various aspects such as spatial perception or orientation.
When we talk about quantitative adaptation, the organ responds to changes in the intensity of light. We have about 120 million rods in each eye, and they are responsible for regulating changes in light intensity, that is, perceiving the difference between light and darkness. The organ sets in motion a physiological mechanism and it is the iris that works by opening and closing, carrying out a process similar to the opening and closing carried out by the diaphragm in a camera lens.
When we talk about qualitative adaptation , the organ responds to contemplation, that is, to the sensations of color , and the retina is responsible for this process. We have around six million cones housed in the retina. Humans have three different types of cones that tune into three different wavelengths: 440 nm, 530 nm and 560 nm. When the cones have the ability to adapt to their respective spectral areas, the eye sends a signal to the brain that develops the phenomenon of color recognition and differentiation, which allows us to orient ourselves in space, as well as differentiate colors even when the lighting changes are drastic, whether there is a lot of light in the space or darkness.
What we mean when we say “color sensation”
The truth is that the perception of colour is conditioned by the spectral composition of the light that falls on an object. The human eye only sees a certain part of the electromagnetic wavelengths, and each colour has a certain frequency (cool colours have lower wavelengths than warm colours). This is why we speak of `body colour', or that when a certain “coloured light” falls on it, a subtractive mixture of colours is produced visually, generating a different colour as a result. (For example: if we project a green light on a red sheet of paper, the result will be different than if we project a white light on the same sheet of paper).
There are exceptions to the perception of the human eye, that is, the famous phenomena of color blindness and hemophilia, which affect almost 5% of the world's population.
