Unfortunately, it is a teaching in the LDS Church, particularly in this passage from the Book of Mormon:
2 Nephi 5:21: And he had caused the cursing to come upon them, yea, even a sore cursing, because of their iniquity. For behold, they had hardened their hearts against him, that they had become like unto a flint; wherefore, as they were white, and exceedingly fair and delightsome, that they might not be enticing unto my people the Lord God did cause a skin of blackness to come upon them.
Essentially, the Lamanites (who
Mormons believe are all the Native Americans and Polynesians) harden their hearts against God and then God (or Yahweh) cursed them with skin of blackness.
If you read the Book of Mormon (it sort of reads like a fanfiction of the Bible) you'll see quite a bit of really racist teachings. It's likely a product of its time since the book was written in the 1820s.