What are the primary and secondary colors? That is an easy question, right? Every child learns early in school that the primary colors are red, yellow, and blue. These colors correspond very nicely to the colors of the rainbow. The familiar acronym, ROYGBV, helps us remember the order: from the outside of the rainbow to the inside, the colors are Red, Orange, Yellow, Green, Blue, and Violet. Notice how the primary colors have other colors spaced between them: orange between red and yellow, green between yellow and blue, and violet (purple) between blue and red (if we imagine the colors looping back around to the start). These “inbetween” colors are there because they are the mixtures of their surrounding primary colors. Thus, red and yellow together make orange, yellow and blue together make green, and blue and red together make purple. That means orange, green, and purple are the secondary colors.
While the preceding description may be familiar to many people, it is actually wrong. For one thing, the primary and secondary colors are complicated by the fact that there are two sets: additive colors and subtractive colors. Also, the primary and secondary additive and subtractive colors contains colors that may not be familiar to most people.
To begin, let us explain what the terms “additive” and “subtractive” mean. Additive colors refer to the mixing of light. It is called “additive” because when colors of light are mixed, they combine to produce a new color. “Subtractive” refers to pigments. Pigments are molecules that reflect light. Take a common pigment, chlorophyll. This molecule produces the green color found in leaves. It reflects green light, but it also absorbs other colors of light. That is an important property of pigments: not only do they reflect light, they also absorb some light. This absorption of light changes the way pigments interact with each other, so subtractive colors behave differently from additive colors.
Let us begin with the additive colors. The three primary additive colors are red, blue, and green. These are the primary colors because combinations of all three of them are capable of producing every other color of light. An important property of the three primary additive colors is that together, all three make white light. If we had three flashlights, one that produces red light, one that produces blue light, and one that produces green light, and we shine all three lights at the same spot, the resulting light will be white. This is yet another important property to remember: white light contains all three primary additive colors.
Now, if we take just two of the primary additive colors and mix them together, we produce a new color called a secondary additive color. For example, say we take our red flashlight and our green flashlight and we shine them both on the same spot. The resulting light will be yellow. In a similar fashion, red and blue light produce magenta (which looks a bit like hot pink) and blue and green light produces cyan (a bit light blue-green, but a little more blue than green). It is important to note that these secondary additive colors, yellow, magenta, and cyan, all contain two primary additive colors. That is, yellow light contains both red and green light, magenta contains both red and blue light, and cyan contains both green and blue light.
What would happen if we mixed all of the secondary additive colors together? Let us consider what we know so far. Yellow contains red and green, magenta contains red and blue, and cyan contains green and blue. If we consider the primary colors, we notice that all three appear in equal amounts, thus yellow, magenta, and cyan light together produce white light. Not only that, but since yellow light contains red and green, what other light is needed to make it white? The only missing primary color is blue. Thus, yellow and blue together produce white light. These are complimentary colors: two colors that together make white light. Notice that complimentary colors always consist of a primary color and a secondary color. The other compliments are magenta (red and blue) and green and cyan (blue and green) and red.
The following illustration shows what has been discussed so far. The primary additive colors are shown in the large circles and the overlaps show the secondary colors and white in the middle where all three colors overlap.
Next post, we will consider the subtractive colors and how they mix with each other.
Written by Steven King
Heart of America Science Resource Center 