Can't purge unused Materials

My model has become sluggish and unresponsive at times so I would like to investigate the following, in case it might be related.

I experimented with a few Materials (solid colors) but did not wind up using them. However, ‘purge unused materials’ does not get rid of them. How can I get rid of them?

This is my first Sketchup model. It is a simple 2D floorplan using 8 Tags and ‘Color by Tag’.
I am using Sketchup Free, Windows 10 (fully updated), Edge Browser / app.sketchup.com
My computer: AMD Ryzen 5 3600 3.60GHz Processor, 16GB RAM, NVIDIA GeForce GTX 1660 Ti Graphics Card, 1T storage.

Any help or suggestions would be greatly appreciated.

Purge unused components first.

Tried ‘Purging unused components’, then ‘Purging unused materials’ and after that the black & white checkerboard square re-appeared as the default material - which is what I was looking to have happen. However, I can’t repeat it.

For example, create a new model, select a color for Material like red, select ‘Select’ from ‘Select’ (to close paint bucket and get pointer), purge unused components, purge unused materials. Result: it does NOT change the default material back to the checkerboard square. Thus, purge unused materials did not delete the selected material (red in this case) even though it was unused. So, how do you get the default material back to the checkerboard b/w square?

You may be over thinking it. The red is simply showing because it was the last colour selected. If you draw any geometry it will be done using the default colour of the model, the white and gray, unless you have changed that.
I think the checkerboard thing is a slight anomaly, you can use the Eye dropper to sample the colour used on the default geometry and the ‘red’ will still show. But I wouldn’t be worried about it, it certainly wouldn’t be causing sluggish behaviour.

OK, thanks for the explanation.