Found a great explanation on this website brochure printing. CMYK stands for Cyan, Magenta, Yellow and Black. These represent the four colours utilised in conventional offset printing. These three colours plus black approximately match primary colours that are blended through the observable spectrum. This is one way printed colours will be made. Adjusting the colours to CMYK will certainly produce the most reliable reflection of what the printing will appear like. Got our prints done with them and it is visually excellent.