I would love to have any of those colors on a diamond and sapphire engagement ring.
Sapphire has a Mohs’ hardness hardness of 9….which is just below that of Diamond at 10.
The minerals that give Sapphire its blue color are Iron & Titanium.
In Violet stones, Vanadium.
Small quantities of Iron result in Yellow & Green tones while small ones of Vanadium produces Orange tones.
Chrome gives you a Pink color.