The primary colors are red, blue and yellow, right? So why don’t TVs and printers just mix those colors to create the rest? Well, frankly, it’s just not that simple.
First, let’s start with those primary colors. The fact of the matter is that RBY is only one set of primary colors, the one that makes the most sense for simple color “math” that our eyes and brains can comprehend. “Yellow and blue make green,” as the Ziploc ad went, is a simple calculation to generate a new color by combining two others. This is what’s called “additive” combination.
While that particular additive set of colors is frequently used for arts and crafts, its closest neighbor, RGB, is used in light projection, such as that of your TV or computer monitor. Here, yellow and blue can still make green, but only after green and red are combined to make yellow in the first place! (visual example ») In the RGB space, black is produced by the absence of colors, while white is produced by combining all of the colors at full intensity. In this way, RGB is the “opposite” of…
CMYK, which is a “subtractive” color space, in which adding color, in this case ink or pigment (in cyan, magenta, yellow and black) reduces the amount of reflection, making the color appear darker. As such, it is the absence of color that produces white (assuming that our foundation is a white surface) and the full combination of colors that produces the richest black (note: while CMYK contains black as an ink, darker blacks are achieved by adding some amount of the other three colors as well).
It’s also worth mentioning, especially when discussing the ramifications of these spaces in graphic design, that their output is far from equal. While RGB devices can produce nearly any color that the human eye is capable of detecting, CMYK falls far short of that (tints of orange and green are especially deficient in this space). This is why it’s important for business owners to see how their artwork appears when it is converted from RGB to CMYK, since much of the artwork’s original richness can vanish in that process. Print designers generally work in CMYK from the start so that they’re never surprised by this color shift.