The Forms Outlet, Inc. - Design Tips: Color Printing

Spot colors are made by mixing basic ink colors together in specific ratios using a formula guide. The formulas are usually assigned numbers, such as those of the Pantone® color system, as shown on the right. Two-color is perhaps the most popular type of spot color printing. Typically, black is used for photos and text, and a second color is used for headlines and other highlights.

Each spot color gets a separate plate. When colors overlap, the color underneath will either be knocked out or overprinted. When a color is knocked out, it will not be printed at all in the area underneath the second color. When a color is overprinted, both colors will be printed in that area. It's usually a safe bet that black will safely overprint any ink. However, because printers inks are translucent, this is not always the case with lighter colors. You may end up with a new combined color you didn't want.

When two colors sit right against each other, trapping is usually required. Trapping is a slight overlap of inks which decreases the effects of misregistration of two plates. The overlap may be as little as a quarter point, or 1/288th of an inch. Here is a good tutorial on trapping.

The Forms Outlet, Inc. recommends that you leave the trapping to us. We can adjust your files to suit our particular press requirements.

The human eye sees the full range of visible light as white light, and it sees subsets of visible light as all the various colors. Our eyes can be tricked into perceiving white light or colors. This is the basis for all color reproduction.

For painters, whose paint is typically opaque, the primary colors are red, blue and yellow. Because printer's ink is transparent, the primaries are cyan, magenta and yellow. Both of these sets of colors are known as subtractive primaries, because they act to subtract parts of the white light reflected from the surface of paper (or canvas, etc.) For example in the image shown to the right, cyan and magenta combine to create blue, and magenta and yellow combine to create red.

In theory, equal parts of cyan, magenta and yellow combine to subtract all reflected light, creating black. However, the reality on press is that these colors alone will not create a good solid black. Plus, full coverage of all three ink colors is problematic in terms of how much ink the paper can handle before getting too saturated. To compensate for these issues, some of the CMY values are substituted with black (K).

The CMYK process is not perfect. In some cases, a spot color is not quite matched with the four-color process. A fifth color - the spot color found in a Pantone formula guide - is added the the printing process.