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Secondary colors are colors created by combining two primary colors together. The exact nature of primary and secondary colors depends on what color system is being used, especially with regard to whether the colors being used are light, pigment, or paint. Each of these systems has different secondary, due to different primary, colors. Regardless of the differences between different forms of color, however, secondary colors are always created the same way — by combining two primary colors.
When discussing colors, whether primary or secondary, it is important to establish the medium in which the color is being utilized. Color can basically be defined in two ways: additive color systems and subtractive color systems. Additive colors are basically colored forms of light, in which combining, or adding, together different colors of lights creates new colors. Subtractive systems refer to pigment or paint, in which color is created by absorbing, or subtracting, certain wavelengths of light, and reflecting other wavelengths that create the appearance of certain colors.
In an additive system, such as colored light from a monitor or projector, the three primary colors are red, blue, and green. The three secondary hues are magenta, yellow, and cyan, which are combinations of each of these: magenta from red and blue, yellow from red and green, and cyan from blue and green. When all three primary colors of light are combined together, they create white light.
Subtractive systems have different secondary colors, depending on the type of system being used. Pigment, which is typically used for printing images, has cyan, magenta, and yellow as the three primary colors. The secondary hues for pigment are then blue, from cyan and magenta; red, from magenta and yellow; and green, from cyan and yellow. As these pigments are combined, they create darker colors, while combining light creates a lighter color; combining all three primary subtractive colors creates black or a muddy brownish gray. It is worth noting that pigment and light have opposite secondary and primary colors.
The three secondary colors often taught and discussed in art classrooms are those based on paint, which is also a subtractive system. Paint uses red, blue, and yellow as the three primary colors and orange, violet, and green as the secondary colors. When combined, red and yellow create orange, red and blue create violet or purple, and blue and yellow create green. There are also tertiary colors that can be created by combining a secondary and a primary color, though these are more rarely utilized.
@Melonlity -- The article has it right. The primary colors for printing are cyan, magenta and yellow. Black is sometimes added in there because it is needed to camouflage imperfections when the three primaries don't combine to render the perfect shade desired.
Also, pure black is regarded as the best thing to use for printing text.
In general, though, black is not a primary color in the printing process. It is added for convenience when it is considered at all.
When it comes to printing, I thought there were four primary colors. That is why it is called CMYK printing. "C" for cyan, "M" for magenta, "Y" for yellow and "K" for black. This article makes no reference to black as a primary color for printers, so the question has to be asked -- is black a primary color when you are talking about printing presses or not?
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