Color vision is an illusion created by the interactions of billions of neurons in our brain. There is no color in the external world; it is created by neural programs and projected onto the outer world we see. It is intimately linked to the perception of form where color facilitates detecting borders of objects.
Color is created by utilizing two properties of light, energy and frequency of vibration or wavelength. How our brain separates these two properties of light, energy and wavelength, and then recombines them into color perception is a mystery that has intrigued scientists through the ages. We know much about the nature of light and the subjective impressions of color, definable by physical standards (Wright, 1946) but ultimately color should be explained at the level of single cells in our brain. Examination of the responses of single neurons or arrays of such neurons provides the best insights into the physiology of color vision. Ultimately our understanding of this process will allow us to model the neural circuits that underlie the perception of color and form. Although still beyond reach, progress is being made in deciphering these clever circuits that create our perception of the external world.
We start by describing the nature of the photoreceptors that convert light energy into neural signals. Then we consider the parallel channels leading from the retina to the thalamus carrying information into visual cortex, where color is ultimately determined. Lastly we use our current understanding to speculate on how visual cortex uses neural circuits to create the perception of color and form.
(http://webvision.med.utah.edu/book/part-vii-color-vision/color-vision/)
For example, a tomato lighted by white light looks red. This is because tomatoes reflect red light. As seen in this example, objects have unique physical properties that reflect or emit light of specific wavelengths. Humans may seem to relate the wavelengths to color in the process of perception. However, this is not the case. Even if we light a tomato with blue light so that red light does not reflect, humans perceive tomatoes as red objects, not blue objects.
(http://www.jp.honda-ri.com/english/projects/intelligence/02.html)
Basic color theory
Color theory encompasses a multitude of definitions, concepts and design applications - enough to fill several encyclopedias. However, there are three basic categories of color theory that are logical and useful : The color wheel, color harmony, and the context of how colors are used.Color theories create a logical structure for color. For example, if we have an assortment of fruits and vegetables, we can organize them by color and place them on a circle that shows the colors in relation to each other.
The color wheel
A color circle consist of red, yellow and blue colors. In 1666 Sir Isaac Newton developed the first circular diagram of colors.There are also definitions (or categories) of colors based on the color wheel. We begin with a 3-part color wheel.
Primary Colors are basic colors, with no mixture of any other color (red, yellow and blue). Mixing them with each other, receiving all other colors.
Secondary Colors obtained by blending equal parts of two primary colors. In this way it appears a green, orange and a purple color.
Tertiary Colors are made from mixture of one primary color and one secondary color. It appears reddish-purple, blue-purple, blue-green, yellow-green, yellow-orange and reddish-orange color.
Some formulas for Color Harmony
There are many theories for harmony. The following illustrations and descriptions present some basic formulas.
1. A color scheme based on analogous colors
Analogous colors are any three colors which are side by side on a 12 part color wheel, such as yellow-green, yellow, and yellow-orange. Usually one of the three colors predominates.
2. A color scheme based on complementary colors
Complementary colors are any two colors which are directly opposite each other, such as red and green and red-purple and yellow-green. In the illustration above, there are several variations of yellow-green in the leaves and several variations of red-purple in the orchid. These opposing colors create maximum contrast and maximum stability.
3. A color scheme based on nature
Nature provides a perfect departure point for color harmony. In the illustration above, red yellow and green create a harmonious design, regardless of whether this combination fits into a technical formula for color harmony.
Color Context
Red appears more brilliant against a black background and somewhat duller against the white background. In contrast with orange, the red appears lifeless; in contrast with blue-green, it exhibits brilliance. Notice that the red square appears larger on black than on other background colors.
Different readings of the same color
If your computer has sufficient color stability and gamma correction (link to Is Your Computer Color Blind?) you will see that the small purple rectangle on the left appears to have a red-purple tinge when compared to the small purple rectangle on the right. They are both the same color as seen in the illustration below. This demonstrates how three colors can be perceived as four colors.
Observing the effects colors have on each other is the starting point for understanding the relativity of color. The relationship of values, saturations and the warmth or coolness of respective hues can cause noticeable differences in our perception of color.
(http://www.colormatters.com/color-and-design/basic-color-theory)
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