A free plugin for both GIMP 2.10 and 3.0 that combines a slightly faded look with gradients of color to enhance photo images.
To install, download the file and place it in the appropriate folder location. You can find this by selecting Edit/Preferences then navigating to Folder->Plugins from the GIMP menu. If you have not already done do, it is much easier to find these folders if you make them visible — in Windows, you can do this from the menu bar in File Explorer.
Install the GIMP 2 plugin directly in this folder. Note that the GIMP 3 plugin must be installed inside a sub-folder with the same name as the plugin. The installation location will looks something like those shown below. Windows:
C:\user\<username>\AppData\Roaming\GIMP\2.10\plugins\gimp_matte_fade.py
C:\user\<username>\AppData\Roaming\GIMP\3.0\plugins\gimp_matte_fade\gimp_matte_fade.py
Linux:
/usr/<username>/.config/GIMP/2.10/plugins/gimp_matte_fade.py
/usr/<username>/.config/GIMP/2.10/plugins/gimp_matte_fade/gimp_matte_fade.py
And that's all there is to it. Open GIMP and you're now ready to go with your new plugin.