There are two colour systems used in design: RGB (Red, Green, Blue) and CMYK (Cyan, Magenta, Yellow, Key). Understanding how both colour models work is essential within the design industry, because the two systems are very different (in fact, they’re complete opposites!). The differences between RGB and CMYK are key to understanding why graphics never print in exactly the same colours as they appear on screen.
RGB Colour System
The RGB (Red, Green, Blue) colour model is used by screens. It’s an additive system, meaning each amount of colour will increase the brightness of it. Therefore, all three colours combined creates pure white.
Each colour has a range from 1 – 255, giving 16,581,375 possible colour combinations.
CMYK Colour System
The CMYK (Cyan, Magenta, Yellow, Key) colour model is used for printing. In contrast to RGB, it’s a subtractive system, meaning each amount of colour will decrease the brightness of it. When you combine cyan, magenta and yellow, you get a very very dark brown. So, CMYK has a fourth ink: black.
Each of the four colours has a range from 1 – 100, resulting in less colour possibilites than RGB with 10,000,000 combinations.
What's the difference?
RGB can easily be converted into CMYK ready for printing, but the difference between the colour systems results in printed graphics appearing slightly (or sometimes, drastically) different to what’s shown on-screen.
One reason for this is that there are fewer colour possibilities with CMYK, so some RGB colours simply can’t be replicated exactly. Because RGB has a greater range of colours, it can produce vibrant and vivid shades that are beyond the range of CMYK, resulting in a darker, duller appearance once printed.
As you can see, when the above RGB image of The Lucky Black Cat Cafe is converted to CMYK, the bright pink shade loses its vibrancy dramatically. Other colours, such as the green plant and the beige latte, appear darker and duller.
Additionally, it’s important to note that colours will always appear brighter on a screen, simply because a screen is brighter than paper/card and backlit for extra vibrancy.
Pantone Spot Colours
One way to ensure a specific colour looks the same as you expect is to use the Pantone Colour Matching System. It’s an Industry-standard method of recreating colours exactly as they appear in the Pantone Colour Guide. Rather than using the four CMYK colours, the 1,000+ Pantone Spot Colours are blended with 14 pigments, expanding the colour possibilities for print. There are also metallic and fluorescent colours available within the Pantone system. Because Pantone uses specialist pigments, rather than the standard CMYK, it’s not available from every printer. It’s also significantly more expensive.