Colors are merely sensations produced by the action of light on the nervous tissue of the retina, which covers the back of the eye.
There are Three Primary Colors en Nature, Blue, Red,-and Yellow. From these are formed all the other beautiful tints which well up from the bosom of the deep, glows in every flower blossoms in the trees, and sparkles in the dew drop; softly stealing from the moon and stars, and written upon the blue arc of night. Red indicates anger, and sometimes guilt. Blue is said to be true, but denotes melancholy and gloom. Yellow indicates cautiousness and prudence, and reflects the most light of any, after white.
Yellow-green is the color nature assumes at the falling of the leaf, and this was worn in the days of chivalry, the emblem of despair. Green denotes tranquility. In heraldry it is used to express liberty, love, youth and beauty, and at one time all letters of grace were signed with green.
The color of all objects depend on the action of those bodies on the light which fall upon them, the different rays of which they reflect, either entirely, or only partially. The light of the sun, and the lights used for illumination, gas, etc., seem to consist of an infinite number of rays, of different color, and however widely they may be spread out by the prism in the spectrum, can.
never be entirely separated, but always form an even gradation of color, from red at one end of the spectrum, through orange, yellow, green, etc., to purple at the other end. Sir Isaac Newton divided the spectrum into seven parts, thinking he could distinguish seven different colors, red, yellow, blue, orange, green, indigo, and violet, which he called primary colors. Sir D. Brewster showed that those colors which Newton considered simple were, in reality, compound, and mixed up with a considerable proportion of white light. He concludes from his experiments that there were but three simple colors, red, yellow, and blue - by the mixing of which the other colors were produced.
The principal advantages attending the choice of red, blue, and yellow, as primary colors, are: That the choice seems to agree with the fact that whenever a ray of white light has one of these three colors removed by absorption, the remaining colors of the ray is that which would be found by an equal mixture of the other two colors. And when a ray has two of its primary colors removed, the remaining color of the ray is that of the third primary color. The color which opposes the strongest contrast to any primary color, is that secondary color, which is formed of a mixture of the remaining two primaries, in such proportion as would form with the first white light. This color is called its complimentary color - colors being called complimentary to each other when they together form white light. For instance, blue has for its complimentary color the neutral secondary orange, formed of a mixture of red and yellow, and this color gives the most vivid contrast that can be opposed to blue. Green is the complimentary, and strongest contrasting color to red, and red to green ; and yellow the strongest contrast, and complimentary to purple, and purple to yellow.
When the colors of the spectrum in a circle, in a perfect gradation all around the circumference, and so that the three primaries, red, yellow and blue, are at points in the circumference equal distance from each other, the strongest contrast to any color will be found at a point on the other side of the circle diametrically opposite to it. Thus, blue will be found exactly opposite to orange, which will be intermediate between red and yellow ; and, in the same way, yellow-green will be found exactly opposite purple-red, etc. Now, as red, blue and yellow are the three primaries, and that all other colors are composed of mixtures of these, let us decide which of the many different colors called reds, yellows, and blues we are to consider as pure, and true primaries. A pure yellow has been decided upon ; chrome-yellow (No. 1), chromate of zinc (citron yellow), or light cadmium. A mixture of any two bright primaries will produce a bright secondary, and any admixture of the third primary will make the secondary color produced much duller or blacker. We consider that would be the purest blue which gave the brightest green with yellow, at the same time that it gave the brightest purple with a red, and it was decided that cobalt blue was the pure primary, which was blue with regard to the yellow chosen. It is obvious that if the blue were a greenish blue, although it might give a very bright green with yellow, it would give but a dull purple with the red. The yellow contained in the blue, and which made it greenish, would blacken or dirty the purple produced, but would not interfere with the brightness of the green. We choose carmine for the primary red as the color which gives the brightest purple with cobalt blue, at the same time that it gave the brightest orange with chrome yellow. Thus we have chrome (No. 1), for yellow, cobalt for blue, and madder carmine for red. These are the primaries.
Colored objects appear colored owing to their action on light. This action consists in absorbing one or more of the different colored rays which fall upon it, and reflecting the rest; and it is these reflected rays that give the color to the object. Bodies which emit light are called luminous, as the sun. Bodies which transmit light, and through which objects can be distinguished, are called transparent, as water, glass, etc. Bodies which transmit light, and not so as to permit objects to be seen through them, are called translucent, as ground glass, etc. Bodies which absorb or reflect all the rays of light, or transmit so few rays that the eye does not perceive them, are called opaque, as wood, metal, etc.
What we call a pure white object, such as chalk or white paper, appears white by reflecting all the light which falls upon it, and is therefore precisely the same color as the light which falls upon it. A pure black object is one which absorbs all the light which falls upon it, and reflects none. Such an object will always appear black, whatever may be the color of the light which falls upon it. Gray objects, (pale black), absorb the three pri-mary rays equally, or in equivalent proportions, but not entirely, so that there is a certain portion of the white light reflected unchanged. A pure green absorbs all the red, and reflects all the yellow and blue. A pale but pure green absorbs only part of the red, and reflects the remainder of the red, together with all the yellow and blue. A dull and blackish green is formed by the absorption of all the red, and also part of the blue and yellow, and the reflection of the remainder of the blue and yellow. The same rule will apply in all cases of all other colored objects, except transparent ones. Silks and satins of either color reflect light.
When three colored rays are mixed together in neutralizing proportions, white light is produced. The easiest way of finding what are the equivalent proportions of the primary colors is this: divide a circle of paper into three equal parts, by lines drawn from the center to the circumference. Paint one of these spaces with pure yellow, such as lemon yellow, or the palest chrome yellow, and paint one of the remaining spaces pure but weak blue, with cobalt, and the other space pure but weak red, with madder carmine. Then try, by spinning the card rapidly on a pivot, whether these colors neutralize each other, and if not, darken that color that is deficient until the gray produced is neutral -that is, of the color of lampblack mixed with white; and when this is the case, the colors on the three spaces will be of the proper neutralizing strength for equal spaces.