As you may have read on another thread here, the black dot is either the liver or gall bladder. Normally on a baby gecko, it can be visable because they are small and their skin is translucent. If the black spots get very large, it means that the liver or gall bladder is enlarged, usually as a response to them not eating. Sometimes it is reversable when they begin to eat, and sometimes not eating starts a series of problems that result in death. I highly recommend buying geckos from a breeder, or, if you buy from a pet store, look for the largest most active one you can.
Aliza
