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Offset Color Requirements

Color is one of the most commonly misunderstood topics in all of printing.  We’ve compiled a few guides to help you understand various aspects of how printed color works, and why it might be different from what you’d expect, so that you can prepare and make sure your colors come out exactly the way you intend.

RGB vs CMYK Color Printing Comparison

Difference Between RGB vs CMYK

The most common mistake we see is creators who submit RGB files for printing.

The RGB color profile combines Red, Green, and Blue light to create colors. It is used by computer monitors, televisions, phones, LCDs, and any device that emits light to create color. It is important to note that since RGB uses light and not ink, it is physically impossible to print RGB files without first converting them to CMYK, which is based on blending ink instead of light.

Converting RGB to CMYK

There is no direct conversion between these two color models, and certain colors that can be created in RGB by blending red, green, and blue light simply cannot be created in CMYK by blending cyan, magenta, yellow, and black ink.  For this reason, we recommend that you convert colors on your end before submitting your artwork files so that you can make any changes you’d like.

We can convert your colors to CMYK for you, but it will inevitably cause shifts in the color palette.  Many printers will just do this conversion without telling you if you submit RGB files, we’ve even heard of printers that claimed they could “print RGB” (which is laughable since it’s a physical impossibility), but at PrintNinja we never alter your files without letting you know exactly what we’re doing.

Another way to create your colors is to use these suggested CMYK values that can reliably produce bright, vivid colors on the printed page.

For a more in-depth explanation of the differences between the RGB and CMYK color models, visit our advanced concepts section.

CMYK vs K

Standard Black vs Rich Black Comparison

As opposed to CMYK, Black-and-white or black-only printing just uses one color of ink: black (also known as key, or K).

The most important difference between CMYK and K-only is that the standard black (bottom of photo) produced using only K will not be as deep as the rich black (top of photo) which is produced using all four colors of CMYK. If you’re converting your files from RGB or greyscale to CMYK, the conversion will often automatically make your blacks rich black.

However, the one time you do NOT want to use rich black, even in a full color CMYK project, is for very delicate lines such as small text.  For example, speech balloons in comic books should use standard black (K only), because with very thin lines, the microscopic variations in plate registration between the 4 colors can cause slight color shadows to appear around the text.

Learn more about Standard Black vs. Rich Black.

Offset Printing Color Matching Spot Color

Color Matching and Spot Colors

Because CMYK blends four colors of ink on an offset press, colors will always exhibit a slight variances between runs and even smaller variances within different copies of the same run.  These variances are much smaller with offset printing than with digital printing, but there will always be minute differences due to the nature of the four-color process.  That’s why colors created by CMYK are sometimes called ‘process colors’.

The only way to guarantee 100% accuracy for a specific color is to use what is known as a ‘spot color’.  In this case, the ink color is mixed separately and applied to the finished document via the offset press using a separate printing plate.  The most common way to specify a spot color for use is the Pantone Matching System, which identifies colors through a number, such as ‘PMS 165’, which is a burnt orange color.

Spot colors can also be used to apply specialty inks like metallic colors, neon colors, or glow-in-the-dark ink.  They are always done via custom quote since their pricing varies based on the type of ink specified and the coverage area.

Please note: it is not possible to match CMYK process colors exactly to a PMS spot color value.  You can look up approximate CMYK values online, which will get quite close, but CMYK printing will always exhibit some degree of variation.

Beware of Extreme Saturation Values

One quirk of offset printing is that very subtle gradients can often get lost, and especially at very high ink saturations, your project may come out darker than it looks on the computer screen.

For single-color saturations, extremely light ink coverage (under 10%) may not even print at all, and extremely heavy ink coverage (over 90%) may just appear to be a completely solid color.

Additionally, if your ink saturation values are too high overall, your project will look much darker than it does on screen.  Deep blues and blacks can look wonderful on a backlit screen, but when your overall ink saturations start exceeding 300% total ink saturation your final product will appear much darker in print.

Here is a saturation scale for ink coverage and an explanation of how to avoid extreme values.

Hardcopy Proofing Is Your Best Option

Let’s talk about the most surefire way to get your printed colors to come out the way you want them: the hardcopy proof.

When you purchase a hardcopy proof you will get a physical version of 8 pages of your project printed on the offset press, which will give you the best possible idea of how your colors will look when printed.  Because of the issues discussed above, this is the only way to know for sure how your colors will translate, and we highly recommend it for those who are new to printing.