Before you explore colors and the various ways to create and apply them in your InDesign document, it helps to have an understanding of exactly how color works, both when you print it and how it displays on your monitor. It's important to know the difference between the various color modes, like CMYK and RGB, and how selecting one type over another can help or hurt your project.
There are two main types of color used in commercial printing: spot color and process color. Spot colors are single-color inks. You may hear a printing project that uses spot color referred to as a "two-color job," with the two colors being black and the spot color (see Figure 29.2).
Figure 29.2. Use spot colors to add a single color to your document as an accent. In this example, our headline is printed in a coffee-brown, giving extra visual emphasis to the subject matter.
Process colors are created by mixing specific percentages of cyan, magenta, yellow, and black, the four ink colors used in color printing. You may hear this referred to as CMYK. The colors in printed photographs, for example, are duplicated based on how cyan, magenta, yellow, and black dots are laid down on a sheet of paper (see Figure 29.3).
Figure 29.3. When cyan, magenta, yellow, and black inks are laid down on top of each other, the four colors combine to create full-color printing. This example displays the cyan, magenta, yellow, and black plates that are combined to create a four-color image.
Spot colors are usually used as accent colors, and spot color printing can often be less expensive than full-color printing, since you are printing with only two plates instead of four. (Note that new printing technologies and the use of specialty spot colors can make an exception to that rule.) Spot colors can also be used at the same time as process colors if you are trying to duplicate a specific shade that cannot be replicated with a CMYK mix, or if you are creating a special effect with the spot color, as with the use of a metallic ink.
If you are using a service bureau or printing company to print your documents, it's always a good idea to have a conversation about color before you send in your documents. They can show you specific samples of both four-color and spot color jobs they have printed and give you advice on preparing your documents for their specific output devices.
Another thing to keep in mind when creating your documents is color display and how what you see on your screen matches up to the printed piece. If you are creating a document that will be viewed primarily on a computer monitor, such as a website or an e-book, you can feel confident that what you see is what your final viewer will see, give or take some variance between displays. If you are creating a document to be printed, however, what you see on your screen can be wildly different from the final printed piece.
The simple explanation is that your monitor displays color completely differently from how color is printed. As stated, the printing process uses CMYK to produce full-color documents. Your monitor displays documents and graphics with an RGB color setup, using red, green, and blue light (see Figure 29.4). The RGB color space's capability of displaying colors is greater than the CMYK's. Therefore, if you're trying to duplicate in print a specific printed color you see onscreen, you should either use a spot color or use a process color from a color library that you have picked from a swatch booklet, for example. Mixing your own process colors can work for you, but is often a chancy proposition because what you see on the screen might not be exactly what prints in your document.
Figure 29.4. This illustration shows the difference between how subtractive color (CMYK, on the left) and additive color (RGB, on the right) mixes and displays.
The final type of color you will run into in InDesign is Lab color. Like CMYK and RGB, Lab colors are displayed as mixes, although in Lab color the different hues are based on the brightness of the various components. You may run into Lab colors when you use colors from Pantone, Toyo, or other color libraries.
An option in InDesign's Preferences window enables you to choose how blacks are displayed in your document (see Figure 29.5). You might be wondering what that's all about. Rich black refers to the color created when red, green, and blue are set to zero. Pure black refers to the color created when the K setting in CMYK is set to 100%. When displayed onscreen, pure black looks more like a dark gray. Use the Appearance of Black pop-up menus to set which black you want to use onscreen and when printing.
Figure 29.5. Use InDesign's Preferences window to determine how pure black and rich black appear in your documents.