Understanding Process and Spot Color

Let's briefly explore the differences between spot and process colors, the two primary ways of indicating color in print documents.

Identifying methods of color printing

Several forms of color are used in printing, but the two most-used ones are process color and spot color.

Process color is the use of four basic colors cyan, magenta , yellow, and black (known collectively as CMYK) that are mixed to reproduce most color tones the human eye can see. A separate negative is produced for each of the four process colors. This method, often called four-color printing, is used for most color publishing.

Spot color is any color ink whether one of the process colors or some other hue used for specific elements in a document. For example, if you print a document in black ink but print the company logo in red, the red is a spot color. A spot color is often called a second color even though you can use several spot colors in a document. Each spot color is output to its own negative (and not color-separated into CMYK). Using spot color gives you access to special inks that are truer to the desired color than any mix of process colors can be. These inks come in several standards. Basically, spot-color inks can produce some colors that are impossible to achieve with process colors, such as metallics, neons, and milky pastels. You even can use varnishes as spot colors to give layout elements a different gleam from the rest of the page. Although experienced designers sometimes mix spot colors to produce special shades not otherwise available, you probably won't need to do so.

There are several advantages to spot colors. You can use colors like metallic inks that are impossible to create with CMYK. Also, your printed results will be more consistent than with CMYK separations, which can suffer from color shift (variation in the hue produced) over the length of a long printed piece. But spot colors work only in objects that have distinct, continuous hue such as a solid brick red that can be printed with just one ink. To produce any image with multiple colors, such as a photograph, you need to use multiple inks, and since printing presses can traditionally print only four to eight colors on a page, you have to mix colors to create the range of hues in such multicolor objects.

Mixing spot and process colors

Some designers use both process and spot colors in a document known as using a fifth color. Typically, the normal color images are color-separated and printed using the four process colors, while a special element (such as a logo in metallic ink) is printed in a spot color. The process colors are output on the usual four negatives ; the spot color is output on a separate, fifth negative and printed using a fifth plate, a fifth ink roller , and a fifth inkwell . You can use more than five colors, however; you're limited only by your budget and the capabilities of your printing plant. (Most commercial printers can handle six colors for each run through the press, and larger ones often can handle as many as eight colors.)

Converting spot color to process color

InDesign can convert spot colors to process colors. This handy capability lets designers specify the colors they want through a system they're familiar with, such as Pantone, without the added expense of special spot-color inks and extra negatives. Conversions are never an exact match, but guidebooks are available that can show you in advance the color that will be created. And with Pantone Process variation, which InDesign supports, designers can pick a Pantone color that will color-separate predictably.

You can set InDesign to convert some spot colors in a document to process colors while leaving others alone. (For example, you would keep a metallic silver as a spot color so it prints with a metallic ink, rather than be converted to a grayish color that is the closest the CMYK colors can produce to simulate a silver. But you would convert common colors like deep blue, purple, and green to process colors, since the CMYK inks can combine fairly accurately to reproduce them.) Or you can leave all spot colors as spot colors, or convert all spot colors to process colors.