The number of melanocytes in all races is constant.They are derived from the neural cells.The colour of melanocytic granules,and their no and distribution determine the color.These granules are donated to our skin cells known as keratinocytes.As we grow older the melanocytes reduce production and thus is the so called grey hair which is the true color of keratin.If the cell incorporates more melanin you get the tan,even rearrangement of the granules are good enough.
Is there any data on how long the lifespan of a melanocyte is?
Also, in regards to the melanin granules, are they like cells containing melanin and the melanin 'deteriorates' over time (as a person gets less tan) or do the granules slough off with other skin cells and they are lost to the body... do they build throughout a persons life, promoting faster tanning?
But then if you can increase the no and quantity of melanin granules ,yes they can get retained.
Cell death or Apoptosis as is known is a programmed one,and I presume body would seek a balance by destroying a few.