RGB and CMYK are the colour processes everyone is familiar with. RGB is an additive process, meaning it adds red, green and blue together in varying amounts to produce other colours. CMYK is a subtractive process. Different parts of cyan, magenta, yellow and black are used to “remove” reflected colours from paper to create other colours we can see. The two processes have different ranges of colour, with RGB providing a more comprehensive array of possibilities.
RGB is used in electronic devices, like computer monitors, while printing uses CMYK. When RGB is converted to CMYK, colours can look muted. As a result, designers were often disappointed when their printed pieces looked different from what they had seen on screen. To avoid this disappointment, printers told designers to convert colours to CMYK so they’d see them more accurately on their computers.
Now, modern workflows allow printers to use colour profiles that automatically match CMYK ink to RGB values to produce similar results. Additionally, commercial digital printers can use inks beyond just CMYK to closely match the wider colour gamut of RGB.
Designers gain some added benefits under this new approach. RGB files tend to be smaller; moving and manipulating smaller files is always easier. Since most designers, today design for print and digital applications simultaneously, keeping files in RGB gives you more flexibility.