I love duochromes of any kind. If it has a hint of a duochrome I am all over it. Well usually. The shifting of colors keeps my attention. Plus they are just cool to wear. I have had Ozotic Pro 504 on my list for a long while. I figured I would never see it. *sniff* Thanks to Jacie at You've Got Nail I have it (and a few others) in my greedy little hands.