When enabled (checked), Custom Target Colors, can affect the values for each color channel (R, G, & B) or the composite RGB. This option is currently only available on the Mac Platform.
This feature is inherited from the Phase One Scanback software. This feature allows the user to increase the values of the shadows and to decrease the values for the highlights when the image is processed in Capture One.
This is possible because Phase One backs offer 14 stops of information. This allows shooters to use the Custom Target Colors to change the values for highlights and shadows. This feature allows for the possibillity to recover detail in the shadows and in the highlights.
This is very useful when you know the printer that you are printing to. Certain printers have a range of values that can be printed. Custom Target Colors allows for these values to be adjusted to the printer's values so that the values of the colors are kept in gamut.
For example when printing on newspaper type paper the dot spreads (dot gain) more than if printing on glossy printer paper. Custom Target Colors can be used to control the values of these channels so that the printer will have an image with the correct values and be able to print the colors correctly.