I like the associated term unobtainium
Meaning the perfect material for the job that doesn't exist lol
I think they are anodised titanium
You can anodise titanium yourselves at home safely using a charger/powersupply and sugar soap as the electrolyte
As you increase the current the tit changes colour from reds through golds pinks and blue ( not correct order, forgotten it ) no dyes needed
So something like 20volts you get purple etc