What is 4-color printing and 6-color printing?

The six-color overprint process is based on the traditional four-color overprint, obtained by expanding the standard four-color unit. But it is different from the hexagonal spot-color process, hexagonal spot-color is based on CMYK with the addition of orange and green, while the six-color overprinting described here still contains only four CMYK colors. The use of six-color process, not only can make the image clarity and resolution has been improved, and the smoothness of the hue excess is also better. Some of the more difficult to obtain colors such as meat color, barbecue food, water color, sky color, chrome yellow and similar metallic colors can be obtained by adding light tones in two-tone printing. Two-tone printing also reduces the appearance of texture in overprints; it reduces halftone dot patterns on the one hand, and expands the range of reproducible shades on the other. With six-color printing, rough halftones appear less rough, with 50 lines/inch halftones looking like 100 lines/inch and 65 lines/inch looking like 120 lines/inch or better.