What are four-color printing and six-color printing?

Six-color overprint technology is based on the traditional four-color overprint, which is obtained by expanding the standard four-color unit. But it is different from hexagonal spot color process. Hexagonal spot color adds orange and green on the basis of CMYK, and the six-color overprinter mentioned here still only contains four colors of CMYK. Using six-color technology can not only improve the clarity and resolution of images, but also improve the smoothness of excessive tones. Some difficult colors, such as flesh color, barbecue food, watercolor, skylight color, chrome yellow and similar metallic colors, can be obtained by adding light tones in two-color printing. Two-color printing also reduces the texture appearance in overprinter, on the one hand, it reduces the halftone dot pattern, on the other hand, it expands the range of reproducible tones. With six-color printing, rough halftone will appear less rough, with 50 lines/inch halftone looking like 100 lines/inch and 65 lines/inch looking like 120 lines/inch or better.