How is it that a brilliant blue logo appears on the screen but duller or darker on paper? The screen and the printer create color differently. The screen emits light while printed color is ink that is reflected light on paper. This is why a screen layout in the RGB color system can be impossible to achieve exactly with ink on paper using the CMYK color system.
To grasp the differences and perhaps learn how to better plan your design, here is an easy task you can do. Open up a small layout containing blocks or images in bright blue, green, orange and purple. Save one copy as RGB and another as CMYK and then place the two files next to one another on the screen. You will likely find that some colors will remain virtually unchanged while other highly saturated colors may appear far less brilliant. The specifics will depend on your design software, the color profile of your images, and the quality and calibration of your monitor, but you should get the general idea. Now you have some sense of what needs to be addressed in your files before you export them to a PDF.
RGB is an acronym for red, green and blue. A monitor creates color by mixing light in various amounts, so the more light that is mixed the brighter the color. As a result, screens can create some vivid green, pure blue and brilliant light shades that no printing press can hope to match using the process colors. For this reason it’s quite possible to create a design with great RGB color that exceeds the capabilities of the printing process.
CMYK is an acronym for cyan, magenta, yellow and black, the four inks printed by an offset press to create the full spectrum of colors found on paper. Because CMYK uses ink to create color, each layer of ink absorbs the light that shines on the paper rather than creating light, so the combination of inks is usually darker. Also keep in mind that not all paper stock is created equal. Coated paper can hold sharper ink and the color may appear richer, while uncoated paper tends to absorb ink more and may appear less vivid. There are additional variables that also play a role in how the printed page looks, such as coverage amounts, the type of color profile and the print system itself.
So, if you create a file in RGB and then convert it to CMYK at the last minute, there will surely be some undesirable changes. A brilliant photograph may look a little less brilliant, a dark image may appear muddy and the distance between colors may become closer together. Rather than passively allowing the conversion of the RGB file to take place, look carefully at the design after converting to CMYK. Review skin tones, corporate or brand colors, dark areas, text in small colors, and RGB effects that are particularly intense. Correct one thing at a time and don’t keep converting the file back and forth between color modes.
A final output should be prepared according to the specification requirements of the print shop. Some print shops will want you to provide a particular color space while others will want a particular color profile used when you create the PDF. A home printer or office printer can be a useful guide to help you assess the layout of the page, but it should not be used as a color reference. Even though it can be helpful to print your page to view it with a real page of paper, the monitor is not a reliable reference device unless it is accurately calibrated. To see how your page will look, particularly if color is involved, you should request a printed proof from a printer that will show your results for paper stock, color density and contrast, ink spread and color shift.
There is nothing you can do to make the colors in the printed piece match the colors in the screen. The better approach is to become familiar with how specific colors will change in print and correct your design with that information, while also having a general idea about what to expect once you go to print. When your file conversion from RGB to CMYK is no longer a big surprise in your design timeline and you understand how your final colors can be affected, that’s when you’re making progress.