Remember way back when mood rings were cool? Well, we still think they're pretty rad (in a funny nostalgic way), and apparently we're not the only ones. Perfect Formula is reinventing the mood ring, but this time in the form of a fingertip fad—nail polish.The top-secret special formula changes your shade from cool colors to warm bright hues depending on your body heat, which triggers the polish to magically transform. And around here, it's no big secret we're big fans of nail art, so this trend may just become our newest obsession. The collection launches in June, so be patient and don't get moody! (Stylelist)