I'm really picky about my Amethysts -- generally, dark, but not TOO dark a purple (you just have to have light be able to get into the stone and bounce back out!) and often with red or blue highlights, depending on the stone and the direction of the light.

This pair of nice deep purple stones are 8mm rounds and set into a 14k gold wraptight leverback earring. The wraptight mounting is essentially a variation on the bezel mounting -- allowing you the most show of stone for the least amount of money.