The Young-Helmholtz theory assumes there are three different types of color-sensitive cones, for short, medium, and long wavelength light rays, which are correspondingly sensitive to blue, green, and red respectively. Science also includes advocates of the Herring theory, which assumes there are four receptor types: two antagonistic systems, yellow-blue and red-green.

The retina’s receptors – the rods ind cones – relay the stimulus through

nerve fibers into the optic nerve and thus into the brain, where the stimulus is converted into conscious vision. By a complex process of physiological-psychological data processing, the recorded color stimulus is transformed into seeing and perceiving color.

We must first assume that we experience color subjectively and thus react individually. It should be noted here that our personal color experience, our responses to, and evaluation of, color always contain an element of the “collective,” which is stored in our “genetic memory.” The effect of color on people is explained by the interplay of physiological and psycho-logical events, by the physical process of seeing color, and the data processing in our brain. It has been scientifically proved that color influences cortical activation (brainwaves), functions of the autonomic nervous system, and hormonal activity. We also know that color evokes certain emotional and aesthetic associations.

The energetic effect of color affects our entire organism. It influences physical procedures. It also affects our psyche, our feelings, thought processes, and emotions. Through holistic associations and parallel sensations within our sensory organization, colors stimulate not only the sense of sight, but also other sensory organs. The intensity of color stimuli and the entire context in which they are perceived play a significant role.

For example, red stands for blood and fire, aggression, revolution, and war, but also life and love. Psychological aspects, especially concerning associations, are often called into question since cultural heritage and intellectual and aesthetic education vary from individual to individual. Re-search using different groups of people has shown, however, that there are in fact collective and individual responses to color associations, which are shared by a majority. Cross-cultural studies and comparisons have displayed astounding similarities concerning preferences, color-mood associations and connotations.

Consequently, color stimulus is always associated with other sources of stimulation as well. The formation reticularis influences the standby state of the entire nervous system, and thus also contributes to controlling attention and aware-ness. Stimulation of the formation reticularis by external and internal factors determines the degree of arousal. It can lead to a simple increase in attention or to visible behaviors.

The formation reticularis tries to maintain a condition of normalcy in a state of stimulation. Stress research has shown that states of sensory over stimulation or under stimulation can trigger dysfunctions in the organism. This is often dis-regarded by designers. It is thus important to adhere to one of the most important, fundamental rules of design – that is, to integrate variation and stimulation into a visual order, and to create a balance between under- and over stimulation.

If a red tone is described as heavy and sweet, it has affected three other senses in addition to sight, that is, touch (weight), smell and taste. The synesthetic effects of color are applicable in a variety of ways. In spatial design, they can in-fluence the perception of spatial dimensions, or compensate for certain stress factors at the workplace, for example, in industry. The expressiveness and effect of a color always de-pend on its respective color tone, which involves its particular saturation, intensity, and brightness, in other words, its hue and nuance. Thus, color tones that are normally seen as warm can be perceived as cooler, such as a very pale red; on the other hand, colors that are considered cool can be perceived as warm, for instance ultramarine.

The impression of coolness and warmth is just as dependent on whether a sur-face is matt, muted, shiny, or polished. Sensing weight is very dependent on the degree of saturation and brightness. Thus, colors that are dark in terms of their own brightness can seem lighter in weight if they are made lighter in color (light violet = lilac); light colors in contrast seem heavier in weight when darkened (dark yellow = brown). For synesthetes, color stimulus can produce other, clear sensory perceptions via sensory channels, allowing them to hear, to feel or to taste colors.

They contribute to our personal experience of color. Color symbolism grew out of the generaliza-tion of color’s effects on the emotions, and the tradition of meanings associated with color. Symbolic and psychological effects of color are thus closely linked. Eckart Heimendahl differentiated between ritual symbolism, traditional symbolism, and the aesthetic-emotional level of symbols, which can also be called the psychological level. These three levels inter-twine, yet each possesses its own significance and expression. Although certain generalizations do in fact merge, in line with an “objectification” of colors, and are then conveyed as symbolic messages, the individual, human color experience still needs to be considered.

Even if many connotations are identical, there are still cultural differences. Green is the color of life for people of desert cultures; it is a holy color in Islam, the color of paradise, and the sign of all material and spiritual things. For people living in forest or jungle, green equally rep-resents life, but also represents a “devouring superpower.” The symbolic meaning of a particular color can be interpreted very differently by people from different cultures.

To understand the symbolic effect and expression of a color, we should also consider whether it is alone or its effect is in relation to something else. The effects of a color can be divid-ed into two important categories:

The absolute or independent effect of color – color as light and luminous radiation

The relative effect of color – on color as a component of the material environment.

The effect of colors always depends on their interaction with objects, and their different design characteristics: the same color, associated with different types of objects, can thus lead to completely different interpretations and opposite impressions and effects. Color effect is prevalent.

As different as the subjective reactions to color may be, color concepts can nonetheless be designed for specific objectives, to suit certain requirements and user groups on a general level. An objective examination of emotional human needs, functional requirements, and the effect of color is therefore unavoidable. In designing the environment, the actual effect of color depends significantly on its materialization, associated with the remaining active role played by environmental factors. The table on next page shows the experimental and phenomenological emotions related to the main colors. It is not a dogmatic codification of the symbolic meaning of color.