Colors and Trapping
Base the colors you specify in your publication on the method that will be used to print it. This will be either Four Color Process (CMYK), Spot Color, or a combination of both. In design applications this is usually referred to as the color mode.
CMYK (Process Color)
The four process color inks are Cyan, Magenta, Yellow and Black. An image printed in CMYK will consist of halftone dots configured in a rosette pattern. The inks are translucent, and when applied in varying percentages, can replicate almost any color in the rainbow. If your application warns you that a color mix you choose is out of gamut, then it cannot be reproduced with four color process. Base your color mixes either on a Spot Color (converted to Process), or an ink swatch book which breaks down the percentages of the four process inks used to make a color. Images in the RGB, Index Color, or some other color mode will need to be converted to CMYK mode to print.
If you want colors defined in different applications to match, make sure their CMYK mixtures match. An imported or placed graphic will bring its color definition with it, so it is often a good idea to define color in the illustration program, then style the elements in the page layout program in that color.
Do not trust your monitor for true color. The color you see on your monitor is a mix of Red, Green and Blue (RGB). So no matter what mode you define your colors in, they will not print in the color your monitor displays.
Scanner software interprets the percentages of color in an original and separates the file into CMYK channels. Each channel can be adjusted independently to improve the interpretation. This is called color correction, and for best results, is performed by an experienced technician.
This method uses pre-mixed inks. Ink manufacturers distribute ink swatch books from which colors can be chosen. Colors have names or numbers (i.e. PMS 281; Cool Gray #10).
Choose your Spot Colors from the Pantone Matching System (PMS) color library. All design applications make this color library available in the color palette. Be sure the color mode chosen is Spot Color, and that color names agree across all applications.
The quickest way to check your color naming scheme is to print color separation proofs and allow the color names to print. For Spot Color, you should get only one page for each color used. Four Color Process prints a separate sheet for each of the four process colors.
Trapping refers to the slight overlap of colors when objects or text touch. Factors such as the type of paper to be used, characteristics of the press, and other considerations will influence the amount of trap required. Therefore, it is best to let your printer set trap.