Click the icon on the right of the bottom panel to activate the gamut check display mode for your image. This function highlights, in cyan, all pixels that are out of gamut with respect to the selected softproof profile. You can also activate gamut check with the keyboard shortcut Ctrl+G. A message “gamut check” on the bottom left of your image tells you that you are in gamut check display mode. Gamut check and soft proof are mutually exclusive modes.
Right-click on the icon to open a dialog with configuration parameters – these are the same as for the soft proof option.