Despite this seems to run counter to some of the information here, though this could simply be that the idea of The Curse of Cain was a popular belief at the time where many Church members might have believed, I actually remember a document I had read while a missionary on the Family and Church History Mission in Salt Lake City.
You see, I went on a non-proselyting mission, approved for only a year because of my mental disorders such as Asperger's Syndrome/Autism. So instead of going door to door and otherwise providing the Word of God to prescriptive members I was given other responsibilities.
This was everything from data entry, mail delivery, to actually delivering documents or files in the Church History Building. I even had the chance of holding some of the Joseph Smith Papers, which I had to deliver to someone.
How this relates to the subject of this thread, is I actually had to deliver a file involving Pres. Kimball going to God involving African Americans receiving the Priesthood and one notable detail in this file is that God specifically told the President that it was NOT
because of the Curse of Cain or Curse of Cain Legacy as it is being called here.
No, that the reasons for doing so was for something else. Sadly, more details were cut off, as if I remember the rest required following a link. Suggesting it was printed off from somewhere… Which admittedly, I probably shouldn't have read this file and it may not be enough to counter everything else here saying it was because of the Curse of Cain, but I felt it relevant as it was something that has stuck with me all these years.
I wish I could provide a link or otherwise provide more information. Yet that is all I have and it was a good 8 to 10 years ago. So I do offer my apologizes on such, maybe I can do some research and see what I can find that could support what the read. I don't know, maybe I should have asked someone about it at the time. Though again, there was the chance it wasn't supposed to be something I was supposed to read. Since I was only supposed to deliver the file.