JOEL - It is clear that in some cases, when a person is especially chosen, God makes exceptions to His own rules. Such must have been the case with Elijah Abel when he received the priesthood.
There is a similar situation in the Bible in The Book of Ruth. Because the Moabites (a white-skinned people who were the descendants of Lot, the nephew of Abraham) did not give food or water to the Israelites when they came out of Egypt into the desert, the LORD cursed them; proclaiming that a Moabite would not enter the Congregation of the LORD until the 10th generation(Deut. 23:3). However, Ruth, a first generation Moabitess, showed such great faith that the LORD made an exception, and she became an Israelite(Ruth 4).
Elijah Abel was ordained to the priesthood office of Elder on March 3, 1836, and to the office of Seventy later that year, because of his faithfulness and because he had helped to build the Kirtland Temple. It is clear from membership records that he received certification as a Seventy on April 4, 1841, and again in Salt Lake City. It is also clear from membership records that he was a member of the Third Quorum of Seventy in 1883, when he left on a mission to Canada. Further, it is clear from his patriarchal blessing that he was to be made (in the words of his Patriarchal Blessing) "equal to thy brethren." Apparently, also, Joseph Smith had told him that he was "entitled to the priesthood," according to Abel's recollection of the event. His Priesthood status is also verified by his Patriarchal Blessing, given by Joseph Smith, Sr., in 1836 (Joseph Smith's Patriarchal Blessing Record, p. 88, as cited in Council Meeting Minutes, 4 June 1879, Adam S. Bennion Papers, BYU, Provo, Utah).
It was Joseph Smith himself who translated the scripture that relates to the denial of priesthood to the blacks(Abraham 1:26-27). But even though he knew this he was apparently inspired by God to allow an exception in the case of Elijah Abel.
Elder Abel was not stripped of his priesthood by Brigham Young but, according to Young's and subsequent church presidents' interpretation of the scriptures, he was denied the ordinances of the temple. However, no attempt was made to remove his priesthood or drop him from the third quorum of the seventies. He remained active in the quorum until his death. President Taylor called him to serve a mission to Ohio and Canada. He returned very ill and died at the age of 83. (Chester L. Hawkin, "Report on Elijah Abel and his Priesthood," unpublished manuscript, special collections, Brigham Young University, 1985.)
It is true that we are punished for our own sins and not for Adam's trangressions. But this punishment refers to that which we receive after this life and after God's judgment because of unrepented sins. We will not be punished for Adams transgression in the next life and the blacks will also not be punished for Cain's sin in the next life. But God can and has placed curses on groups of people, including their decendents, in this life from time to time, as illustrated by the experience of the Moabites I refered to earlier.
We still suffer from the curse that God placed upon the earth as a result of Adam's falling(Moses 4:23-25). Cain's curse was to live as a fugitive and a vagabond and that the ground would not yield fruit for him(Gen. 4: 11-15), and for reasons only God knows, the curse included denial of the priesthood to the decendants of Cain until at a later time when He determined they were ready to receive it.