If we're considering racial connotations, I don't think so. The term 'race' in CoC2, like in most other sci-fi and fantasy works, refers to species rather than ethnicity, so the stereotype 'dark-skinned people have larger cocks than light-skinned ones' (off which BBC content is based) probably doesn't exist, and the closest stereotype would be 'minotaurs, marefolk and [whichever other species apply] have larger cocks than other species'. That doesn't preclude the existence of a human character in CoC2 that has both dark skin and a large cock (especially given that alchemy is capable of changing skin tone, cock size and even species), but I'm pretty sure those two traits won't be associated with each other.