Diamond or gemstone centre into my three stone mount?

[pearaffair]

Decided to continue the convo here:

Which colour centre?

I’m slowly narrowing it down! I’m leaning towards green or purplish. What do you think? (Visual aid thanks to washable markers lol!) would that be green tourmaline for green, and tanzanite for the purple? Hmm!

www.pricescope.com

Since I have decided on a coloured stone centre.