There are only three places (that I know of) in the scriptures that speak of this subject: Moses 5: 40 (34-41)
, Moses 7: 8 (6-12)
and Abraham 1: 24, 27 (21-27)
All three of these scriptures deal with previous dispensations. Since this is a new dispensation, what is written in previous dispensations is not binding upon us. That is the general rule. However, in this case, the doctrine of blacks being denied the priesthood is actual church doctrine (or was church doctrine prior to '78) in this very dispensation. The reason is this:
The First Presidency has the absolute right to officially interpret scripture. Those passages above have been interpreted by every First Presidency to mean 1) that the "mark" of Cain was a skin of blackness and the characteristics of the negroid race, 2) that Cain and his seed were cursed with this mark and that they were also denied the priesthood in this life and all the blessings of the temple, 3) that the Canaanites were decendents of Cain and partakers of this curse, 4) that the blood of Cain and the Canaanites was preserved through Ham (Ham's wife) and 5) that this curse has never been rescinded by the Lord (until '78.)
When the First Presidency officially interprets scripture we are never presented with their interpretation for a vote. They do not need to present a revelation to us in order to interpret scripture. It automatically becomes official church doctrine. An example of this is the Word of Wisdom. The Lord in the revelation states "hot drinks" which could mean anything, except that the First Presidency has officially interpreted that passage to mean "tea and coffee." This "tea and coffee" interpretation has not been presented to the church for a vote (that I know of), it is merely official church doctrine by virtue of the fact that the First Presidency has this right of scriptural interpretation and they have exercised it.
Every First Presidency has interpreted those passages exactly the same way. Could the interpretation have been incorrect? Possibly. Whenever Joseph had a question about something, he would go to the Lord and ask and the Lord would give a new revelation concerning the matter. It does not appear that this was done with the curse of Cain doctrine. Each subsequent First Presidency re-interpreted or re-affirmed the previous interpretation of prior First Presidencies concerning those passages.
President Kimball, however, felt different. He interpreted those passages just like his predecessors did, but instead of leaving it as it was, he petitioned the Lord constantly to "lift the ban" and he apparently received a revelation that it be lifted. Now, we the people of the Lord's church were never presented that revelation, we were only presented with the results of that revelation: that the ban was now lifted.
Any doctrinal changes have to be approved by the saints through the law of common consent. The saints at that time consented. Had I been a member in '78, I would not have consented. I would have demanded to have the actual revelation received read to the conference for approval. But the saints, in typical "follow the prophet" drone-like behaviour, merely accepted an official declaration instead of the purported revelation it was based on. And that OD is now binding upon us.
I find it strange that the revelation itself was not presented. Could it be that the revelation read something like this?: