RGB colour profiles
RGB has three primary colours of light: Red, Green, and Blue. Electronic devices like computers and tablets combine these three colours to produce all other colours on a screen.
RGB is an additive colour profile because you create new colours by adding primary colours of light together:
Green light + Blue light = Cyan
Blue light + Red light = Magenta
Red light + Green light = Yellow
Red light + Green light + Blue light = White
The RGB colour gamut (i.e. the range of colours within a colour spectrum) has a broad range of colours because it essentially mirrors how our eyes see colour. Our retinas receive red, green and blue light, which is then processed in the brain and allows us to see an array of colours.
Of course, this all depends on one key factor: light. Printed matter doesn’t generate light - it reflects it. So how do you reproduce colour in print if with no light source? The answer is you need to subtract colour, which is where CMYK comes into play.
CMYK colour profiles
CMYK stands for Cyan, Magenta, Yellow and Black (the K stands for Key). Unlike RGB, where you create colours by adding two or more together, CMYK is a subtractive colour profile, so you remove a primary colour of light from any white light that hits it.
White light, like daylight, appears visible to the naked eye, but it’s not void of colour. White light occurs when all colours in the visible spectrum appear in roughly equal amounts. By altering these amounts, we can subtract wavelengths and produce different colours:
- Cyan ink reflects Green and Blue light - but not Red
- Magenta ink reflects Blue and Red light - but not Green
- Yellow ink reflects Red and Green light - but not Blue
To produce the three primary colours, you have to think in reverse:
- Cyan and Magenta combined only reflects Blue light
- Magenta and Yellow combined only reflects Red light
- Yellow and Cyan combined only reflects Green light
Imagine you have a piece of white paper - it’s white because it reflects every wavelength of light. Using Cyan, Magenta and Yellow in different proportions, you subtract specific colours of light to produce a wide range of colours.
You should get Black by combining Cyan, Magenta and Yellow. But our eyes perceive colour the RGB way, meaning CMY doesn’t produce a perfect result. To combat this, we add black ink. It will absorb all light and provide darker tones and richer blacks.
Converting RGB to CMYK
Since the CMYK profile works on a subtraction theory, its colour spectrum is limited compared to RGB. Primary light colours (pure red, green and blue) will often appear less vibrant when converted to CMYK.
In the image opposite, you can see the gamut of available colours with several RGB profiles and those available with CMYK.
Please note that uploading RGB files to our print ordering system will be automatically converted to CMYK values. We believe our conversion system is accurate, but we recommend creating your specific CMYK colour for printing to avoid disappointment.
How to stay in the CMYK gamut
In Photoshop, InDesign or Illustrator, an out-of-gamut warning may pop up in your Colour Picker tool. If you see this triangle with an exclamation mark, it will inform you that your chosen colour may not print accurately with CMYK.
While the program may suggest a similar colour that does appear within the gamut, we have also compiled a list of recommended CMYK colour values which should print consistently.
Working with RGB and CMYK profiles
Everything printed on paper will have a CMYK ink colour profile. And anything created for on-screen viewing will have an RGB colour profile. But you should make and print your designs in CMYK.
However, if you created a webcomic, you would design it in RGB for better web viewing. If you want to print your webcomic, you need to convert your artwork files to CMYK and manually adjust any colours that may not look right. Creating artwork in CMYK for online projects can restrict the creative process due to limited colours.
To get an idea of how your RGB project will appear in CMYK, switch to CMYK Mode in Photoshop or InDesign. Then you can easily see which colours may need adjusting.
If you are using a colour profile, use GRACoL2006_Coated1v2 (download it here) - this is our preferred CMYK profile. If colour accuracy is vital to your project, you can order a proof to see how the final prints will look. And if you have any questions, contact our team of print experts via email, phone or in the Messages tab of your pending orders - we’re always here to help.