the problem youre having cant be fixed with the vmf. what youre reffering to as "the purple" are missing cubemaps, you can fix this yourself by compiling cubemaps on your map. heres a tutorial that tells you how to do it https://tf2maps.net/threads/tutorial-building-cubemaps.16452/
the only other way to get rid of them is to edit the source texures, which is far more complicated to do than just compiling cubemaps.
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