The differences between RGB and CMYK colour for the rest of us

You’re working with a designer or ad agency on a print project. During the design phase, you’ve been seeing and approving PDFs. Once the print job is complete, you get printed samples. Wait! The colour in the final printed product is vastly different than what you approved.

Why? You’ve had a shift in colour models. Your monitor, which works on an RGB colour model, can duplicate many more colours than what can be achieved in traditional 4-colour process (CMYK) printing.

Here’s a simplistic explanation of the differences between these colour models for us non-techies.

RGB Colour Model (wikipedia)

RGB (Red, Green, Blue) is the colour model that runs most things digital…monitors, TVs, cameras, etc. It’s an additive colour model, meaning the more red, green and blue you add, the closer you get to white. A 32-bit monitor can display approximately 16.2 million colours.

CMY Colour Model (wikipedia)

CMYK (Cyan, Magenta, Yellow, blacK) is the colour model used when printing using a traditional 4-colour process method. It’s a subtractive colour model, meaning the more cyan, magenta and yellow you take away, the closer you get to white (when printing on a white substrate). Or reversely, the more cyan, magenta and yellow you add, the closer you get to black. In theory, adding 100% each of Cyan, Magenta and Yellow equals blacK, but in practice you get a muddy dark brown. Black (or K) is added to get clean, true blacks. In CMYK process printing, approximately 3.125 million colours can be achieved.

RGB and CMYK are related, though. Here’s a great demonstration of RGB and CMYK colour models and their relationship from digitalArtform.com:

Many other factors can skew colour perception as well. I’ve discussed some of these in a previous blog.

If colour is critical to your printing project, ask to see printer proofs. It will take a little extra time before going on press, but can save money and time on the back end. Proofs are cheap. Reprints are expensive.