This is an extremely sensitive and subjective issue and I anticipate my answer may or may not cause some people to feel alienated, offended or rejected. I extend my apologies in advance. However, this is the definitive answer to the question what is a light skinned black person.
Light skinned people, in particular, are native english speaking fair skinned people. mulattoes (first generation children of one white and one black parent) are generally accepted as first class light skin due to the prevalence of lots of aristocratic european looking features such as a prominent nose, straight to mildly curly hair and blue/green/lighter colored eyes while also blended with and bearing desirable African features such as strong slender, well coordinated, sexually appealing bodies, and smooth/unblemished skin. The following is a summary of the social classes resulting from mulatto marriages. If a mulatto marries and has children with a white person, their children would be considered quadroons or possibly octaroons; these children are not generally accepted as light skinned as their affinity for white people is likely to be too strong. if the same mulatto person marries and has children with a dark skinned black person, their children are black; these children are not accepted as light skinned because their cultural affinity for dark skinned black people will be too strong. if two mulattoes or descendents thereof marry and have children, especially near the third generation and beyond, their children are TRULY light skinned, also lesser known as Blue Veins. For a background description of a blue vein, please read the Wife of His Youth by Charles Chesnut.
Therefore, A light skinned person is not truly established and accepted as light skin until they have been confirmed by their mulatto parents or an official social society such as the Blue Vein Society that is intended to protect and promote the interests of light skinned people. Neither Black, nor White nor Hispanic peoples, regardless of how easily they assimilate, are accepted in these social circles because of the extreme sensitive nature of the race issue in America and how it affects the descendents of mulattoes.