True colours

What is the difference between RGB and CMYK?

This is something that you may have heard bandied around if you’ve ever had to get something printed or artworked. If you’re only after a quick rule of thumb, in a nutshell RGB is needed for all things digital (web, TV, mobile/tablet etc) and CMYK is for all things print (whether professionally done or that rubbish printer you have at home). Though, knowledge is power after all. So if you’re after a little more info, they needn’t be unknown, scary terms. Let’s break them down. 

The acronyms themselves simply stand for the colours used within the various ‘processes’. RGB becomes Red, Green and Blue, with CMYK becoming Cyan, Magenta, Yellow and blacK (with the K being used so as not to confuse people with the blue in RGB). They both do the job, but as the mediums they’re going to be ultimately used on display colours differently, different models are needed. A quick crash course on why below.


Screens are made up of (depending on your resolution) millions of pixels, each displaying a colour. These pixels are even further broken down into the sub pixels of RGB. Yes, the screen you are viewing this on is actually millions of tiny little sets of three, a red, a green and a blue light, all being tuned together perfectly to create the colours you’re seeing. 

Artboard 9.jpg

RGB itself is an additive model, meaning that you add more colours to get lighter colours. As you can see from the above image, when combining all three at full brightness, you get white. So if you could zoom into a white screen enough to see the sub pixels, you would actually see millions of little sets of red, green and blue lights, which our eyes and brain are perceiving as white. Insert mind blown meme here.


Now the above system obviously wouldn’t work for print. RGB works as you’re shining light through the colours to give you the various shades, which is obviously not an option for say, a book… That is why CMYK is needed here as it is a subtractive model, meaning that rather than using all the colours to create white (as RGB does), it uses none of them and creates white by subtracting colours. 

Artboard 9 copy.jpg

As you can see from the above, darker shades are achieved by using more colours, which again is the opposite of how RGB does things. The three colours together create a darker shade, with black being used sparingly to give things a little extra 'weight'. This allows for all the necessary colours to created when printing anything, as the four of them are simply mixed in the correct quantities to create the desired shade.

The logical problem when printing

As you may have realised then, how can you be sure of the colours you need for your CMYK print materials, when you’re viewing everything in RGB? It’s a problem that plagues the design world and I have many a horror story of people sending big print runs of things, only to find the colour is completely wrong.

This is where the various colour matching systems have to come into place and print tests are conducted beforehand, to make sure any artwork is printing properly and a good match. There are other options available (like Pantone colours), which we’ll get into in another post, but as a rule of thumb, it’s always a good idea to check before sending off a large volume of printables.

So, If you have any questions or misgivings, always feel free to give your printer or designer a shout and they should be able to point you in the right direction. Better safe than sorry!

ResourcesDan Spencer