There is a consistent issue in printing with deep / dark blue tones as printed on the sheet and compared to the colour specified on the designer’s screen.

CMYK vs. RGB

The issue arises from the core difference between CMYK and RGB colour spaces. To clarify; RGB stands for Red, Green, Blue, which are the primary colours of light, and used to create the images you see on your monitor, tv, etc. RGB is an additive colour space, which means that colour will become brighter when more light is added. When all three primaries are combined at full intensity, white is created. RGB is measured typically from 0-255 on all three values. With black being 0R/0G/0B and white being 255R/255G/255B.

CMYK (Cyan, Magenta, Yellow, Black), conversely, is a subtractive colour space. When no ink is present the “colour” is at its brightest, because only the brightness of the paper shows through. As ink is added to the sheet, the paper brightness is dimmed until it is eventually black. CMYK is typically measured in a percentage of coverage, from 0C/0M/0Y/0K to 100C/100M/100Y/100K.

What this means, in the end, is that the two methods will be able to produce many of the same colours, but there will be some on the fringes that will not be possible. We see this most often in the deep and bright blue colours.

When you design your project on your computer screen, and you want to see a bright blue colour, you may be tempted to choose the brightest blue available to you, which would be 0R/0G/255B. The problem you would find, is that any time you use a high value primary from either space without balancing them with the other primaries, you will find yourself “Out of Gamut”. This means that while the colour may display beautifully on your screen, you are looking at a colour that cannot be reproduced on the page.

The greatest bias between the two is actually along the green colour axis, fortunately, 255 G is such a bright, slime green that it is rarely used in design elements. Deep Blue or “Reflex Blue”-style colours in the Pantone Colour Chart are far more commonly requested.

What Can Be Done?

Some design software will have gamut warnings built in. They are not perfect, as different printers will have different equipment with different fringe gamut colours. However, if Photoshop doesn’t give you a colour gamut warning, you have better odds of seeing your colour represented on the page correctly.

To check for gamut warnings, select your colour and view it in your software’s colour picker. Typically a small warning sign will appear next to colours that are out of gamut (see above for the Photoshop version of this warning). In the example above, there is a small patch of colour underneath the warning sign that is clickable and will substitute the colour you have picked in your palette for a similar colour that is within the print gamut.

Another option is to reason out your colour choices. If you choose a blue that is built from 100% Cyan with 90% Magenta to give it more depth, odds are your colour is going to print in purple. What you are seeing on screen is an RGB representation of a CMYK colour build, and that is not always an accurate view. BE AWARE: small desktop inkjet printers use a different type of ink with a different shade of Cyan Magenta and Yellow than large production machines, and have different RGB to CMYK drivers built in to them and therefore cannot be trusted to proof your colour.

Finally, if you are doing a lot of design for print, you can have an RGB monitor calibrated to display the CMYK gamut as best possible. This is the best way to ensure that your colours are being selected properly, though this is typically a paid service, and as before, CMYK gamut can vary slightly from printer to printer.

At the printing stage, it is sometimes possible to correct these issues by lowering the print density of a colour. We prefer to save this practice for emergency use only, as this is a global change, and can make faces appear too yellow or green when the magenta levels are lowered. This method also will not change the amount of magenta in your blue, but the intensity of the magenta used in the entire project. Therefore, lowering the density will not necessarily create the desired colour, but will bring it somewhat closer, though at the expense of the rest of the piece.

Best Practices

The best practice is to start your job in CMYK, and if you have RGB images, convert them early and be aware of the CMYK values used to create the colours. If you see a lot of Magenta in your Blue build, consider bringing it back a bit. As an example, when trying to get a nice deep blue for the Winnipeg Blue Bombers, we look for about 65%-70% Magenta with 100% Cyan.

Also don’t forget that every monitor is different. What you see on your screen will not always be exactly the same as what the person on the other side of your email will see.

If you are ever unsure, always feel free to ask for a printed sample to confirm that your finished piece will match your expectations. We are always happy to print a copy from one of our digital machines to check colour. Upon request, we can even use the machine and paper that your job will be done on to ensure the highest accuracy possible. If your project is going on one of our larger offset presses, we can also schedule a “press-check” so you can come down and see the first sheets of your project come off the machine. As always, we welcome questions and feedback, so don’t hesitate to contact us.

Matt Gemmell is the Art Room Supervisor at Dave’s Quick Print and has been in Prepress and Design for over 10 years.