Products may be printed in two or more colors by almost all of the processes described earlier. The simplest method of color reproduction is flat-color printing. A separate plate is prepared for each color desired. Plates are then printed in sequence on a single sheet of paper. Each plate is covered with the desired color ink and then printed in register with all of other color images. The process-color printing method is used to reproduce full-color pictures such as the colored comtinuous tone photographs. Process-color activities include: color separation, color correction, and color reproduction.
A beam of white light passed through a glass prism results in a rainbow of color. This is because white light is really a mixture of all the colors of light. Each color refracts or bends differently as it enters and leaves the prism, Figure 7-29.
Three colors of light-red, blue, and green-can be used to reproduce white light, Figure 7-30. Where all three colors of light overlap, white is produced. Red, blue, and green are called additive primary colors bcause added together they form white light.
Where any two additive primary colors of light overlap, a third color is formed. Red and blue to form magenta. Blue and green form cyan. Red and green combineto produce yellow. Magenta, cyan, and yellow are called subtractive primary colors because they subtract colors from white light to form black. The subtractive process is shown in Figure 7-31.