About neutral density

You can control neutral density from the Trap section of refine process templates.
All inks used for printing do not have the same darkness. For example, yellow is lighter than cyan. Neutral density is used to specify the darkness of a printing ink on paper. A neutral density of 0 is white (no ink). For process colors, the neutral densities vary, depending on the ink set (for example, EuroOffset, SWOP. For spot colors, neutral density can be explicitly specified. If a spot color is normal (non-opaque), neutral density can also be estimated from a given color.
Example of neutral densities for process colors:

The neutral density of a non-100 percent value can be calculated from the area coverage (0-100 percent) and the neutral density of the ink. The neutral density of a composite color is the sum of neutral densities for all of the separations.