Tips & Tricks - Colors

Defining Colors: RGB vs. CMYK vs. Spot


Color is the single most confusing subject in printing. Here is the minimum that you need to know:
What RGB is about - TVs and computer monitors actually only display red, green, and blue colors. But when those colors are combined in various amounts, the human eye is fooled into "seeing" other colors. (This is what makes color TV practical. It only has to be manufactured to make three colors).

What CMYK is about - Printers, on the other hand, do NOT use red, green, and blue ink (or toner) to show color. They use cyan, magenta, yellow, and black (referred to as CMYK) ink in various combinations to accomplish the same thing. Using CMYK is also known as four-color process printing.
Why do TV/monitors and printers have to use different methods to produce color? Because of a BIG difference between the nature of a TV and the nature of a printed piece of paper. TV's make their own light. They "emit" light, and the RGB light rays are "additive". But ink doesn't make light, it ABSORBS light rays of certain colors and REFLECTS light rays or other colors. The light itself must come from somehere else(room light or the sun). We say the ink on paper "subtracts" light.
RGB light rays can be "added" together to make other colors. CMYK inks can be mixed to "subtract" light waves so that when white light bounces off the inks, the colored light rays you don't want are absorbed, and the colored light rays you do want are bounced to your eyes.
What Spot Color is about - When you offset print with specific colors of ink other than CMYK, this is referred to as "spot" color printing. Kind of like, "Let's put a spot fire-engine red ink right in the middle of the page. That will get people's attention!"
In general, this method is less expensive, and more color accurate, when you only need 1, 2 or sometimes 3 colors of ink. The fewer the colors, the less expensive it will be. The major limitation of spot color printing is that you can't print full-color photos (which require CMYK). But if you don't need full-color, spot can be the way to go. Spot colors can be specified exactly from a color library, the most common of which is the Pantone Matching System (PMS). If you choose PMS colors, you and your printer will know exactly what colors are expected, because you can see samples of them in a PMS book.
Why you care about RGB v CMYK v Spot - The best color model to use in your file depends on what's in it and how you plan to reproduce it. It's best to make this choice at design time, not after you bring your files to the print shop.
For instance, if you intend to do spot color printing, make sure you actually define your colors as spot in your program. Otherwise, it can be very difficult and expensive to go back later and convert it.

One of the most common problems is submitting RGB files. These must be converted to CMYK or spot before we can offset print them. As a result of the conversion, the colors will change somewhat. Sometimes the change isn't significant. Other times, it is (either the colors become dull, or shift to noticeably different shades). So it is best to convert them yourself first, to get a better idea of what you are likely to end up with.
This brings us to another gotcha: Programs like Microsoft Word aren't capable of specifying color other than RGB. If you intend to print a colored Word file using offset printing, your printer will have to convert the file in some way. This may cost extra and delay getting your job done. Call us to discuss your job if you want to create it with Word or a similar word-processing program.