Nowadays, even in apps on handheld devices that the general public are using you get the choice of CMYK and RGB, and where the majority of people using these apps will just ignore them, it is really important to know the difference if you are doing any kind of website design or graphics for printing within your business and when to use which for best effect.
RGB = Red, Green, Blue
The RGB colour mode uses these three base colours to form just about every other colour you can imagine as red, green and blue are called ‘additive colours’. This means that the RGB colour mode creates other colours by combining (or ‘adding’) different quantities of red, green and blue e.g to create a yellow colour, you combine green and red, for light blue, add green and blue. Although more sophisticated than this overview, modern home printers know how to combine these colours in varying amounts to ensure that you end up with the exact colour you want. The process is the same for computer monitors too.
Computer monitors and other displays use the RGB colour mode along with LCD/LED TV’s and most cameras and digital scanners too, mainly because it offers the widest range of colours with great accuracy.
CMYK = Cyan, Magenta, Yellow, Key (black).
CMYK works in an entirely different way to RGB as instead of using ‘additive’ types of colour, it actually uses ‘subtractive colours’ (Cyan, Magenta, Yellow and Key). Key is another name for black.
When you combine all the colours of the RGB colour mode (red, green and blue) in varying amounts, you end up with the colour white (i.e. the most pure combination). With the CMYK colour mode, all of the colours are subtractive and therefore, the more colours you add together, the darker the colours are going to become. Eg magenta plus yellow (or more precisely subtract yellow from magenta) equals a bright red colour, subtract yellow and cyan, you would end up with the colour green. So, simply put RGB and CMYK are really working in opposite ways.
Printing has a limited printing range and so people will often think that something looks different once printed than it looked on screen, and this is due to the different colour ranges that printing onto paper and viewing on screen allows.
So the main thing that you need to decide when you are choosing between RGB and CMYK is what the output will be. If the output will be viewed on a computer monitor or a mobile phone/device etc, then RGB will be your colour system of choice whereas if the design is to be printed, CMYK is the standard and best option. CMYK is still used by most professional printing companies so if you’re looking to get something printed professionally, you need to be aware of this.
Most of the time you can safely create your designs in RGB and simply convert your project to CMYK near the end of the design just before you send it off to the printing company. By doing this, you’ll be able to create your design with the full RGB spectrum which will give you a lot more choice in the way of colours.