Color is tricky at the best of times. If you want exact color management for your book cover design (such as a particular shade of blue for a university logo), you really should use something called spot color. Spot colors are specially mixed ink colors. Like the paint you purchase for your walls, spot colors, or Pantone Matching System (PMS) colors, are mixed according to predetermined recipes. Each color in the PMS spectrum has an assigned number. When a client picks a number, the ink is mixed according to that recipe. It’s usually more expensive than process color (4-color) digital printing, which I will explain in a moment. If you are using an offset press though, the fewer colors you have, the lower the cost, so going with spot colors could be beneficial. The most common ink choice would be black and one or two other colors (although you can have more than that if you choose, but as you add colors, the price increases). Black is necessary in most cases, since both your interior text and your bar code will need to be black.
Process color is the most common choice for book cover design and all book cover designers are familiar with process colors. Process colors are commonly known as CMYK colors. C (Cyan) M (Magenta) Y (Yellow) and K (Black) are the four colors of ink that are mixed together to come up with the colors you see on your book cover. With digital printing (also called print-on-demand or POD), it’s usually necessary to use this color system.
It’s important not to confuse what you see visually as only one color, or four colors, or 10 colors, with what the printer will consider to be one, two, three or four colors (some presses can handle more than four). Your cover may have a solid pink background with black text, but still be a four color cover. That is because all four colors, CMY and K, were used to create your particular shade of pink or black. See the image below, which demonstrates what I mean using cyan.
Now it gets more confusing. Aside from PMS colors and CMYK colors, computer screens can only read and show you something called RGB colors. The RGB stands for Red, Green and Blue. While CMYK colors absorb light, RGB colors reflect light. What this means is that in the CMYK gamut, absence of all color (C at 0%, M at 0%, Y at 0% and K at 0%) will produce white (also called reverse). That is why CMYK colors are called Subtractive – the more color you subtract, the whiter the color. However, with RGB it’s the opposite. The more color you add, the more white you have. RGB colors are called Additive. The white on your computer screen is actually 255 Red, 255 Green and 255 Blue. If you add into the factor that computers are also being lit up from behind, monitors vary, screen settings and operating systems and software varies between programs and between user settings, which anyone can change, you can understand why trying to judge what a color will look like in print while viewing it on a screen can be tricky. The only way to ever know for sure is to either go into the print shop and choose a color from their color swatches, or wait until the printer sends a print proof. Even the color sample I pasted in is actually only an RGB rendition of the CMYK colors. And yes, even the CMYK in PhotoShop is only a close, RGB representation of the CMYK colors.
To be honest, it’s rarely an issue. The colors are pretty close and most experienced book cover designers and printers will be able to help. It’s only in areas where you need to have an exact match, such as a university logo color, as I mentioned earlier, that you may want to get more hands-on with color management. Your printer will probably be able to supply you with the CMYK code or PMS number that you need and you can give that to your book cover designer.
There are things to watch out for though, especially if you’re switching from the RGB color gamut to CMYK “on the fly.” Meaning, you’re letting the program just handle it and come-what-may. Industry-standard programs such as those produced by Adobe and Quark are fine, but I’ve seen some people actually create covers in programs developed by Microsoft. Since most Microsoft programs only work in RGB, color management is an issue. Some shades of blue, green and pink are particularly difficult. Below you will see an RGB repesentation of what can happen when proper color management is not employed. Although this is dramatic, it is pretty much what happens with this particular shade of pink. CMYK colors are often more subdued than their RGB counterparts. The CMYK color range is smaller, plus the absorption of light can really impact things.