Does everyone have the same amount of melanin?
Genetically, everyone is born with the same amount of
"Melanocytes", or the cells that produce melanin. It is your global
background that dictates how much melanin you eventually will have
in the skin.
Example: Typically those whose background stems from ancestors
who have lived closer to and south of the Equator have more melanin
in their skin. Where those whose background is from ancestors that
have lived in the Northern Hemispheres typically do not tan and
have less melanin in their skin. Conditions such as Albinism and
Vitiliago also may also compromise the amount of melanocytes in the
body.
Melanin by definition is two fold...one is olor coloring and the
second is protection from UV.
Another topic that might help with understanding your question
is the "Fitzpatrick Scale"