What Is an ACO File?

Adobe Photoshop is likely the app you need to open ACO files

What to Know

  • Some ACO files are color files used by Adobe Photoshop.
  • If it's not a color file, your file could be a project used by ArCon.

This article describes two file formats that use the ACO file extension, including how to open both types.

What Is an ACO File?

A file with the ACO file extension is an Adobe Photoshop color file that stores a collection of colors.

Some ACO files may instead be project files used with the ArCon architectural software, but we have very little information on them.

ACO files in Windows 11

ACO is also short for technology terms that are unrelated to a file format, like analog central office, average communication overhead, and access control object.

How to Open an ACO File

ACO files that are color files can be opened with Adobe Photoshop in a couple ways:

  • The easiest method is through Edit > Presets > Preset Manager. Change Preset Type: to Swatches and then choose Load to browse for the ACO file.
  • Another way is to access the Window > Swatches menu. On the top right of the small window that opens (probably to the right of the program) is a button. Select it and then choose Import Swatches or Load Swatches.
Import Swatches menu item highlighted in Photoshop

When looking for the ACO file you want to open, make sure the file type filter is set to ACO and not ACTASE, or anything else.

While you can make your own custom swatches in Photoshop (through the Save Swatches option using the second method above), the program does include a handful of them when it's first installed. These are located in the \Presets\Color Swatches\ folder of the installation directory and are automatically loaded when the program opens.

The name of each color is also saved in this file, which you can see by hovering the mouse cursor over the color in the Swatches window in Photoshop.

The online image editor Photopea can import ACO files, too, through a similar swatches menu as Photoshop. Open that panel through Window > Swatches, and then select Load .ACO from the panel.

ACO project files are associated with software ArCon (planTEK).

If you find that an application on your PC does try to open the file but it's the wrong application or you'd rather have another installed program open it, you can change the default open program for ACO files in Windows.

How to Convert an ACO File

This is a special format used only in Photoshop, so there's no reason to convert one to any other format. In fact, Photoshop can't even see/browse/open the file if it's saved under a different file extension, so converting it would be useless.

Although ACO files are an exception, in this case, it's normally true that you can use a free file converter to convert one file format to another like you can with popular formats like DOCX and MP4.

Project files like those used by ArCon are normally saved in a proprietary format that's only useful within the program that created them. Plus, given that it's a project file, it likely holds other things pertinent to the project like images, textures, etc., so it's unlikely that it can be converted to some other format.

Still Can't Open It?

If your file doesn't open correctly with the programs described above, double-check the file extension to confirm that it really does read ".ACO" and not something that just looks similar. Some files share similar suffixes, even though they're not related and can't be opened in the same way.

ACF and AC3 files, for example, are strikingly similar but shouldn't be treated exactly like ACO files.

AC files are another example. They use a file extension that's just one letter off, but are actually unrelated to Photoshop and ArCon. Instead, AC files could be Autoconf scripts or AC3D 3D files.

  • How do I save an ACO file as an ASE file?

    In Adobe Creative Cloud, go to the Swatches panel, select the Menu icon in the upper-right corner, then choose Export swatches for Exchange. Saving the ACO file as an ASE allows you to open the file in other Adobe CC programs like Illustrator.

  • How do I add a swatch to an ACO file?

    Import the ACO file into Photoshop, then select to Plus (+) in the lower-right corner. You can then go to Menu > Export Select Swatches to save a new ACO file with the included swatches.

Was this page helpful?