Colour guide for printing

When printing, it can often feel like making the colours do what you want them to do is an impossible task. However, by exploring different aspects of printed colour, and understanding its many quirks, you can fast-forward to getting it right every time.


The difference between RGB and CMYK

Our system does accept RGB colour files and automatically converts them to their CMYK equivalents for printing, but the colour conversion is not always perfect.

Any technological device, whether computer monitors, TVs, phones or LCDs, use an RGB colour profile. This is because an RGB profile uses red, green, and blue light to make the different colours – there’s no ink in sight. To reproduce RGB files in print, you have to convert them to a CMYK format. Instead of blending light, this format blends Cyan, Magenta, Yellow and blacK ink to make the piece more printer friendly.

For more information on the differences between the RGB and CMYK colour models, please read our detailed explanation.


We have also created a list of suggested CMYK values to help ensure bright, vivid colours when printing.

CMYK values and formula charts

The RGB colour model
The RGB colour model
The CMYK colour model
The CMYK colour model

Converting RGB to CMYK

Unfortunately, RGB can’t be converted to CMYK directly. When switching from light to ink, some RGB colours become impossible to reproduce in CMYK. If a printing company claims they can print in RGB, alarm bells should start going off!

This isn’t to say that RGB to CMYK conversion is impossible. Our conversion guide will step you through the process in a convenient, easy-to-read format. When you successfully convert your RGB files to CMYK before submitting any artwork, you will have full colour control when printing, including manually adjusting tricky colours.

How to convert RGB to CMYK

Colour model menu options
Colour model menu options

Standard black vs. rich black

Offset printing has two main ways to produce black: standard black and rich black. Standard black is standard because it only uses black (the K in CMYK). Rich black, on the other hand, uses a mix of Cyan, Magenta, Yellow and blacK to create a richer, more intense colour.

It’s worth noting that, when converting from RGB or greyscale to CMYK, you will automatically end up with rich black.

There are occasions when it is better to use standard black, not rich black. This is particularly important if have very fine lines, like small text or speech bubbles in comics. Even in a full colour CMYK project, you should always use standard black. Otherwise, you run the considerable risk of ‘ghosting’, where the four ink plates needed to make rich black produce microscopic variations that result in a blurred shadow of unwanted colour.

To find out more about standard black and rich black check out our comprehensive guide.

Standard vs rich black printing

You can also check out our guide on full colour vs black and white, because sometimes it’s actually better to print blacks in Full Colour in order to get your blacks really black.

Colour vs black and white printing

The RGB colour model
The RGB colour model
The CMYK colour model
The CMYK colour model

Colour matching

Colour can look different on your screen compared to a printed page, because screens are backlit, whereas print reflects colour. Your choice of paper and finish can also affect the appearance of your colours.

For best results, we recommend printing on silk paper, while uncoated paper will produce slightly muted colours.

CMYK always blends four colours of ink (cyan; magenta; yellow; and key, or black), which can produce very slight colour variances between runs, and incredibly small colour variances within different copies on the same run. If colour is critical to your project, please get in touch with our print experts and we’ll give you the guidance you need to get the results you want.

Learn more about colour variance

In offset printing, very subtle colour gradients can get lost, especially when ink saturations are very high. When this happens, your artwork could end up looking darker than it appears on the computer screen.

If your ink saturation values are too high overall, the printed result will appear darker than expected. This is especially true with deep blues and blacks. They may look incredible on a backlit screen, but will appear much darker in print if your overall saturations begin to exceed 300%.

In the case of single-colour saturations, light ink coverage under 10% may not print at all, while coverage over 90% may turn out as a solid colour.

Have a look at our saturation guide for ink coverage. It explains how to avoid extreme values and make sure that every detail of your print can be seen clearly.

Ink saturation and density

Spectrum of colour samples