Amethyst
I'm usually a big fan of amethyst jewels (my birthstone), but I can't get behind this parure.

And here's another emerald tiara, usually it's Marie Astrid who wears it.
The necklace is beautiful, but the tiara is weird. It needs some height to it, or it needs to be worn flat like a headband.

The citrines work because the center stone is larger than the others, so it gives illusion of height. The amethysts in the tiara are all the same size.
I like most of their jewels except for that cheap looking butterfly thing Linus wears, and those rubies that Claire has worn. The rubies look cheap and gaudy and Linus' tiara looks childish and cheap. I also dislike that gigantic tiara that MT wears (is it called the Societe Generale tiara?). The tiara is nice but it looks terrible on MT. It needs to be worn with big, bouffant hair like Beatrix wears or like Frederika of Greece wore with her big tiara. MT just doesn't ever have the right hairstyle for that tiara when she wears it. Big tiaras need big hair.