Hmmmm... Maybe you are just mixing up wheither its hearts are empty or full. I believe (this has worked for me, but I'm not positive it's correct so don't be mean) black means full. And pontiac2lover, they can die before one year old.
they only time a tama cannot die is in the baby stage; that first hour. after it evolves into a toddler, it can die.
as for dieing 4 times in one day bunnygotchi, you may have just had a string of bad luck. try waiting to start a new one until a saturday so that you have the whole day to watch and take care of it. also, resetting before you start may be a bit of help too.