this happened to me twice i got a mametchi without realy trying on the music star and i once got a kuromametchi from a non perfect care teen on the tamago h34r:
Oh, well, it's kinda hard to explain but check this site, it might be helpful. There are many versions of tamagotchi, the one called v3 looks like this.
And besides, this whole forum is about tamagotchis... :mimitchi: