
It would have been much better if they allowed users to edit the themes and share the user created themes online. Unlike some other popular image viewers, FastStone Image Viewer does not allow any custom third-party themes or icons for its toolbar. In case of a portable version of FastStone Image Viewer, the settings are saved inside the same folder where the FSViewer.exe is located. If you are using an installed copy of FastStone Image Viewer in Windows, then its settings are saved in the user profile folder for the user who is currently using the computer. The gray theme looks like the older color settings from Windows XP times. The bright theme is the default theme and shows the interface in a much more modern style. The dark theme is almost black and looks very much like the dark mode of Windows 10 user interface.

These themes can be enabled to match FastStone Image Viewer window with the dark or light modes of Windows 10 user interface.

Now starting with the version 7.5, it comes with three themes – dark, bright and gray. It supports all the known image formats, many digital camera models and offers a host of image editing and management features.

FastStone Image Viewer is a free and fast loading image viewer for Windows.
