Images on a monitor are composed of light-emitting diodes in the form of pixels. However, printers work with paper, which is not made up of light and pixels. Printers are forced to work with dyes and pigments to replicate colours on paper. Each device uses different technology to create the finished product, sometimes resulting in mismatching colours.
Computer monitors use RGB colour modes to create colours on the screen, while printers rely on CMYK colour modes to put these colours on paper. RGB mixes the primary colours red, green, and blue in different quantities to create the colours on your screen. The RGB gamut is composed of every colour that exists in light, therefore the pixels on a monitor can each display almost 17 million colours. CMYK, on the other hand, creates colour by combining four base colours: cyan, magenta, yellow, and key (black) in varying degrees. This limits the distinct colours that can be created using CMYK to only a couple of thousand. Colours from your monitor are being converted from RGB to CMYK during the printing process. Because of the technology they rely on to print, printers cannot replicate all of the colours a monitor can display. CMYK’s limited colour options often times yield duller and darker colours than those you see on your screen.