File with a .ACO extension contains a collection of predefined colours and their names, utilised in Adobe Photoshop. Along with the installation files, in the Presets/Color Swatches/ directory, there are colour samples of the ANPA, FOCOLTONE, HKS, PANTONE, TOYO, and TRUMATCH standards .

ACO files are used during creation of graphics which has to correspond to specific colour standards. For instance, they are useful during preparing printouts of photos to be displayed. Names of the colours of a collection are displayed in the program in the moment when a mouse cursor hovers over a given colour within the pallet.