Every day I click http://www.thebreastcancersite.com to fund mamograms for poor women - it's free to me - and there are the inevitable ads. Today I noticed an ad for a bracelet with Dichroic stones.
Looked it up and it is a substance that absorbs light according to the direction from which light comes. Or. Having a different color depending on which direction it is observed from.
Just adding to your fund of word lore.