This issue was caused by a bug in version 2023.0. It was fixed in version 2023.1, but once the issue has occurred, updating will not help.

The problem

When clicking on the house icon in the Colors palette, you get an empty list, even if the model has a lot of materials, see image below.

The solution

1. Close SketchUp (Go to SketchUp > Quit Sketchup
   
   
2. In Finder, go to the Go menu > Go to Folder...
   
3. In the window that appears, type: ~/Library/Colors
4. In the folder that opens, delete all the clr files:
5. Then restart SketchUp and the problem should be fixed!