For example, to print green, there is no direct green in the four primary colors of CMYK. If we want to print green with four-color ink, we can only print a proper proportion of yellow after blue printing, and then press it on the original blue ink, so that the color we see is green. This is the color printed by color ratio superposition, also called four-color printing. For spot colors, the blue ink and yellow ink are mixed before printing, and the green color is prepared in advance, and then printed in the Mo Dou of the machine, so that the green color can only appear once, instead of the corresponding color produced by the superposition of the two colors like four-color printing.

Introduction of four colors: Four colors, namely CMYK, also known as printing color mode, is a color mode that relies on reflection. Similar to RGB, CMY is the initials of three printing inks: cyan, magenta, magenta and yellow. K takes the last letter of black, and the reason why it doesn't take the first letter is to avoid confusion with blue. Theoretically speaking, only three kinds of CMY inks are enough, and these three kinds together should turn black. However, due to the current manufacturing process can not produce high-purity ink, the result of CMY addition is actually a dark red.

Introduction of spot color: Spot color refers to the color that is not printed with C, M, Y and K, but printed with specific ink. Spot color ink is pre-adjusted by printing factory or produced by ink factory. For each spot color of printed matter, there is a special color plate corresponding to it when printing. Using spot colors can make colors more accurate. Although the color can't be accurately expressed on the computer, you can see the accurate color of the color on the paper through the pre-printed color swatch card of the standard color matching system such as Pantone color matching system, thus creating a very detailed color swatch card. For the non-standard spot colors set in the design, the printing factory may not allocate them accurately, and the accurate colors are invisible on the screen, so if it is not a special demand, don't use your own defined spot colors easily.