Please in the name of that is good and holy in this world do not take what is said on BIg Love as what the mormon church believes. We are not polygamists, if you are in the church and you practice polygamy, then you are excommunicated. I have heard that Cains mark was his black skin, but that doesnt mean that white people are better or that black or people of colored are more sinful or anything like that. It just means that his mark was his black skin
That doesn't appear to be consistent with what Mormon leaders have said in the past:
Church leader Bruce R. McConkie, on the denial of equality for Africans:
“NEGROES IN THIS LIFE ARE DENIED THE PRIESTHOOD; under NO circumstances can they hold this delegation of authority from the Almighty. The gospel message of salvation IS NOT CARRIED AFFIRMATIVELY TO THEM... “NEGROES ARE NOT EQUAL WITH OTHER RACES WHERE THE RECEIPT OF CERTAIN SPIRITUAL BLESSINGS ARE CONCERNED...” (Mormon Doctrine, 1958, p. 477)
Future President of the Mormon church, Joseph Fielding Smith wrote:
“Not only was Cain called upon to suffer, but because of his wickedness HE BECAME THE FATHER OF AN INFERIOR RACE.”
(The Way to Perfection, page 101)
More from Smith:
“There is a reason why one man is BORN BLACK and with OTHER DISADVANTAGES, while another is BORN WHITE with great advantages. The reason is that we once had an estate before we came here, and were obedient; more or less, to the laws that were given us there.”
(Doctrines of Salvation, Vol. 1, page 61)
The Mark of Cain
The Mormon prophet Brigham Young on the appearence of Africans:
“Cain slew his brother....and the Lord put a mark upon him, which is the FLAT NOSE AND BLACK SKIN...”
(Journal of Discourses, Vol. 7, pages 290-291)
From a Mormon Publication:
“Their skin is quite black, their hair woolly and black, THEIR INTELLIGENCE STUNTED, and they appear never to have arisen from the most savage state of barbarism.” The Juvenile Instructor, Vol. 3, page 157)
http://www.realmormonhistory.com/god&skin.htm