One of the first lessons you learn in kindergarten—once you’ve mastered the fundamentals of sharing, saying “please” and “thank you,” and asking to go to the bathroom—is understanding the primary colors. To kindergartners, with their bottles of goopy tempera paint, the concept is simple: red, yellow, and blue. However, as it so often does, the “everything I ever needed to know, I learned in kindergarten” axiom fails us in the graphic design world. We learn later that green can be a third primary color and that yellow really takes its place as a primary color among magenta and cyan. This is because there are multiple color models and color spaces beyond the traditional primary colors. If you’re still stuck in that early childhood mindset, we’ll explain some of the differences between color spaces here.
An additive color space is one in which adding primary colors together at full intensity yields pure white against a black background. Additive color models find use in lighting and electronic displays such as the one from which you’re reading this very article. The most popular color spaces to use additive color are based around the primary light colors of red, green, and blue, with the standard RGB space—or sRGB—being chief among them.
Further developments in light testing have since yielded the Adobe RGB space. As the mind behind industry-standard graphic design programs such as Photoshop and Illustrator, Adobe sought to strike a balance between additive and subtractive color with an additive color space that could also faithfully represent the profiles of its subtractive counterpart.
While additive models are based around bringing together colors of light to form white on a black background, subtractive color space models bring together colored inks to form black (or a rough approximation thereof) on a white base. The most common model of subtractive color is the cyan, magenta, yellow, and key-black model, which we know better as CMYK. These are the inks that are in everything from your personal inkjet printer to mass-scale printing presses. Rather than give off light, compounds in inks selectively absorb light, giving our eyes the perception of different colors.
Color vs. Chromaticity
One of the biggest challenges that upstarts face in learning the differences between color spaces is making the distinction between color and chromaticity. After all, “chromaticity” appears to just be the Greek word for “color”—nothing more than an uptown synonym for the same concept. However, while cylindrical color models such as hue-saturation-value work in three dimensions, chromaticity concerns itself only with hue and saturation, meaning that an application concerned with chromaticity cannot truly include many colors familiar to us, such as brown or gray. No color space or model can truly incorporate every color except for perception by the human eye—the widest color model of all.