Swarovski crystals are a perfect match to the original gems of G2 ponies. Adult pony: size pp18 (foiled, XIRIUS chaton 2.4 mm) Baby pony: size pp14 (foiled, XIRIUS chaton 2.4 mm)
Underneath you can find all G2 ponies (adult and baby) sorted after the color of the gems in their eyes.
Press the links below for a gallery of the ponies with each color gem in their eyes.
I’m unsure whether Fuchsia or Amethyst is the best match for some of the ponies with dark pink/seemingly purple gems, though most of the time Fuchsia seems to be the right match. Under this link is some of the ponies that might be better matched with Amethyst.