I think what I have is a bug in the Materials window (which shows up as Colors on a Mac).
The summary:
Without the user realizing, he may see a user list in the Colors window (aka Materials window) on a Mac that is really a *.clr file in ~/Library/Colors, and not in the default SketchUp location of ~/Library/Application\ Support/SketchUp\ 2017/SketchUp/Materials/ . Furthermore, this list won’t work to save new textures, and may even be causing hangs on quitting the application if the user tries to add a custom texture to it. All of this is not only nonfunctional, but opaque and puzzling to the user.
SketchUp should either ignore ~/Library/Colors/ files, or let the user know that saving textures here will not work (and not just fail and hang the application.)
Details:
In the Colors (aka Materials) window, I found a List there with my name on it, which I had apparently made a long time ago. Since I’ve used to use SketchUp a few versions ago, I figured this was my custom list and started adding textures to it.
The problem is, that between quitting and restarting SketchUp, none of these new textures would be persistent. Furthermore, at least 50% of the time when I quit SketchUp, it would hang indefinitely and I finally had to Force Quit it, causing a crash report.
After trying to do a clean uninstall/reinstall, I finally found that the list with my name on it was actually ~/Library/Colors/Matt.clr. New Lists from the Colors (aka Materials) Window are saved in ~/Library/Application\ Support/SketchUp\ 2017/SketchUp/Materials/ . I believe this was the source of my problems.
When I made a new List, it appeared in the proper directory ~/Library/Application\ Support/SketchUp\ 2017/SketchUp/Materials/ , and textures saved to it successfully.
SketchUp should either ignore ~/Library/Colors/ files, or let the user know that saving textures here will not work (and not just fail and hang the application.)