What is 4 color process?
Four color process is a method of printing whereby 4 translucent inks are overlapped to create a wide array of colors. This process is ideal when printing on a white garment, because the white in the garment, along with the translucency of the inks, is what makes the colors bright. (If you print on a dark garment, the results will not be the same) Four color process, is the same method used to print colorful magazines and most colorful images on paper, like posters, flyers, etc.
Printing on garments is a bit different, in that, the surface is not as smooth as paper, but it can still yield a bright and colorful print. In some cases, additional screens are added for emphasis or for effect, these screens are known as spot colors.
Four color process works best on a smooth white garment. If your garment is ribbed or has a deep grain, that will take away from the print.
The next time you want to print an image or design with many colors on a white garment, the 4 color process may be an option to consider.