I think I would do amethyst. Purple is further from green on the color wheel than blue is.
Actually, *I* would do the blue because it's my favorite color, but that to me sends a definite ocean vibe. I think the amethyst is more balanced with your collection, and would be more versatile. It looks more like "jewelry" (jewel tones). UNLESS you have a strong attraction to blue or if blue would work better in your wardrobe. Get the blue if you cannot stop thinking about it.
The orange isn't doing anything for me. I love coral too, but it is very close to skin tone so it doesn't show up as much, and it doesn't seem to go with the style of the bracelet as much. Plus, orange with green reminds me of an orange tree. It might be better as a third or fourth color.
JMO. Any of them would be beautiful.