MacOS – Missing dock icons

If restarting and all that doesn't help, here's how i fixed mine.

1. Open finder.
2. Go to /Applications.
3. Drag the offending application to the desktop to create a shortcut.
4. Shortcut should have the proper icon.
5. Right click shortcut and click on Get info.

6. Click on the icon on the top left of the info view. Example:

   

7. When icon is selected (blue highlight), hit Cmd+C to copy it. Example:

   

8. Delete shortcut (not necessary).

9. Go back to /Applications in finder.
10. Right click on the offending application.
11. Click Get info.
12. Notice the place where the icon should be Top left.
13. Click on that location to highlight it.
14. Press Cmd+V

You should now see your icon again.

Tip: This method can also be used to change any icon to something else and customise your Mac !

I don't know how to dim inactive icons in the Dock. However, some people prefer the old-style two-dimensional dock that you can activate. It's certainly easier to discern which apps are open on this view.

To activate the 2D dock, open Terminal. Then type in the following command:

defaults write com.apple.dock no-glass -boolean YES

From there, you can log off & back on, and your Dock will have changed. If you ever need to revert this setting back run the above command again, but change the word YES for NO.