A technique used To make the color more intense. Or the like, the color looks heavy. To highlight the contrast And see the difference in weight and color. Often used in step 4 of coloring. From the colors to the weight of the rain intensity as needed. The weight should be evenly tinted. If you want to see a difference in the dark with the light. Causes shadows on different pictures out. If the dark throughout the image. It has a sharper prints.