Color theory can be confusing for many people. We all learned about "primary" colors, but why are those specific colors dominant in culture over any of the others? In this tutorial we'll demystify the science behind color theory, specifically additive and subtractive color, and show you how you can put this knowledge to work in a practical way.
Basic Color Theory
Strictly speaking, color theory is a set of practical guidance for mixing colors with the goal of creating color harmony. I could go on forever listing all of the nuances that fall within this category, but let's cover the two most popular versions.
The first principle is that like colors will go with each other, which makes complete sense. Designing an all-red room? The deep reds and the orange-reds will go together. Designing a blue room? The deep royal blues and the sea blues will all go together. If you're designing an all-blue room, however, and throw in one neon pink chair, it will clash, and you lose the harmony of the room.
The second principle is that complementary colors (colors on opposite sides of the color wheel) will go together.
Take a look at almost any sports team, and you can see these two principles in action. Seattle Seahawks? Blue and green are right next to each other on the color wheel. Denver Broncos? Blue and orange are across from each other. Green Bay Packers? Yellow and green are next to each other. My alma mater, the University of Washington Huskies? Purple and gold. You get the idea.
On Screen With Additive Color
Let me burst your brain. There is no such thing as white light. "But if there's no such thing as white light, what are we doing with white balance?" Technically, the color of light is defined by the wavelength of that particular spectrum of light. There's red light, orange, yellow, green, blue, and violet. When you look at a color wheel it rolls back into red. So where is white? When you see a light that appears white, what you are seeing is an equal mix of all the other colors.
How do you get the color black? With additive color, black is simply the absence of light. You get different variations of colors by mixing different light wavelengths, and when they get equally mixed, you end up with white. This model is exactly how your monitor works. It's also why we all edit photos in RGB color space. Our content is going out on the internet, viewed on computers phones and tablets, and even our print shops do digital printing, so RGB makes sense as a color standard.
If you take a closer look at that color wheel above, hopefully you'll think that it conflicts with everything kindergarten told you about primary colors, and you would be right. We all learn early that the primary colors are red, yellow, and blue. We were taught the only way to get green is to mix yellow and blue, when actually, green is its own wavelength in the color spectrum. So how did we get all mixed up thinking about primary colors?
Welcome to the RYB (red, yellow, blue) color model. For centuries, painters considered red, yellow, blue, and green to be the four primary colors. When you look at the camera raw panel, it makes a lot of sense.
Under white balance, you have blue and yellow on one slider, and green and magenta (pretty close to red) on the other.
Isaac Newton, famous for everything we know about gravity, did experiments with light and prisms, and determined that red, yellow, and blue can be mixed to create all other colors. He was a pretty smart guy, and this theory has now become dogma, which is taught in our primary schools, despite the mountain of evidence that it's wrong. Sticking with the RYB color model would yield an even smaller color gamut than any other color mode we use.
This chart is the main reason we teach that red, yellow, and blue are primary colors. Anyone else see a problem with this color chart? The name of each color is misrepresented. The blue is actually more cyan. The red is actually more magenta. Take a look at the inner petals. You very clearly see red, green and blue. And most importantly, the middle is black, not white. Which brings us to...
In Print With Subtractive Color
Unlike additive color, which is all about light, their respective wavelengths, and combinations of wavelengths, subtractive color is all about the light that isn't there. A screen shows you an image by creating light in a specific color. A print shows you an image by creating a surface that absorbs all of the lights of various wavelength spectrums except the one it reflects, which is what you would call that color.
The RYB color space may be awful, but its cousin, CMYK, is incredibly useful. Red ink works to bring us a red image by absorbing every other light spectrum and reflecting the red one. The basics for this model are cyan, magenta, and yellow. (The "K" stands for black.)
Because this works by blocking the light with substrates like paint or ink, this is the preferred color space for most printers. With photo labs that print digitally, even if they are still calibrating and looking at your photo in RGB, then there is some under-the-hood CMYK conversion happening to get you a final output.
Applying Color Theory on Set
Tired of looking at color wheels? Me neither! (Just kidding.) Let's look at how you can use this knowledge practically.
You can apply additive color theory when you are using multiple lights with gels. Think about how the lights will mix with each other, and you can create a whole room of colors from just a few lights with deliberately placed gel combinations.
Likewise, you can use subtractive color theory when you are making those gel decisions. Don't have a Rosco gel pack with millions of choices? (First of all, you should, because it's only $10.) You can get a lot more choices out of your gels by overlapping them to create new colors. The one downside to this is that you will lose power as you add more gels. Need a green background, but only have yellow and blue gels? Finally, I'm glad kindergarten taught me something.
Applying Color Theory Inside Photoshop
Inside Adobe Photoshop, you usually don't have to worry about adding light or blocking light. But knowing color theory can help you get better colors.
Here is a rough outline I did for a composite I worked on last year when I was in Hawaii. As you can tell, each photo has a color cast, but the color cast for each is different. If I'm going to create a cohesive piece, these all need to have the same colors.
If you have the Info panel open in Photoshop, then it will show you the RGB values (or CMYK values, if you work in that color space) for any particular area of an image.
I picked one photo that looked as if it had the right color cast and made that my "control image". I looked at the RGB values in the Info panel and tweaked each of the other images using Color Overlays until I was seeing similar RGB values in my new photos. You can do this by going to Layer > New > Fill Layer, and choosing a color that is on the opposite side of the color wheel from the one you are trying to correct for. Then lower the Opacity until the RGB values read the same.
By understanding how all the colors work together, I was able to adjust every underwater photo to match the control image. Once everything matches, then it's just a matter of blending using layer masks and a brush, and applying creative color adjustments on top.
In this tutorial you've learned the basics of color theory. You now know how additive and subtractive colors work, and you've seen some examples of how you can use this theoretical knowledge to create better photographs.
When has a deeper understanding of RGB and CMYK helped you in your photography? I'd love to know in the comments.