I always liked both versions! Lovely

I've seen the glass ones go entirely bright purple. Quite an interesting effect though I've never seen one powered on in that condition.

Yeah I think it is due to a chemical used in the glass as it ages - it does create an interesting effect when lit

Unusual - One would expect glass to be as static as materials get...

Yes as far as I know it is caused by sunlight reacting with the glass (solarization) causing them to get progressively more purple. I installed one outside on a sunny wall 10 years ago and it has become noticeably more purple in that time, similarly I have one that has been used indoors all its life and the glass is still 100% pure white in colour.