Ancestry Resources

I know most Jamaicans are of African descent but what percentage of those people have any kind of European ancestry. (For example, 1/4 white or 1/8 white)

I am asking this question because Jamaica and Haiti both are predominately black nations but it is still possible to tell the difference between them.
Jamaica has a higher frequency of brown and light skinned people than Haiti, even though most people in both nations are darker skinned black people.

I know that sometimes the white babies are born with a certain birthmark that shows in some part of their ancestry that had a black parent. What is the name for this brand of birth, and what you usually think? My boyfriend has high marks on his arm that look like coffee stains and is very dark, so I think I may have black ancestry somewhere, but his grandmother is Sicilian.