The Book of Moses records that "the seed of Cain were black and had not place among them."
Old Testament Revision 1 [Moses 7], The Joseph Smith Papers website, accessed August 11, 2021
And the Lord said unto Enoch behold mine abode forever and Enoch also beheld the residue of the people which were the sons of Adam and they were a mixture of ale [sic] the seed of Adam save it were the seed of Cain for the seed of Cain were black and had not place among them