Dear, I've discovered that nail poolish in the current German Vogue issue. It works like the well known mood-rings which change their colors according to your moods (but actually to your body's temperature). In some way I'm a fan of things like that.
If you want to you can check the website:
Oh, before forgetting to mention: do you know that movie "Aquamarine"? It's rather a typical teenage-movie, but its story is great. There you meet this mermaid, who also has nails which change their color. I think the "phenomena" became real...