This is fascinating, and also concerning. I do not understand someone teasing relatives for being darker skinned. (I don't understand anyone teasing anyone for that, really.) I don't understand the OP's friend telling her "goldilocks, you aren't mixed", either, but people who identify as black mistreating each other because they are "too black"? Don't most minorities, "black" or otherwise, have enough backward "white" people treating you poorly for that reason? Why perpetuate that on each other?? And over skin pigment levels??
Of course I get teased by fellow "white" people for being too pale. And white people are always comparing tans and bragging if they win they "who's darker" contest. How's that for ironic?