"And that they had altered and trampled under their feet the laws of Mosiah, or that which the Lord had commanded him to give unto the people; and they saw that their laws had become corrupted, and that they had become a wicked people, insomuch that they were wicked even like unto the Lamanites (people of color)."
-- Helaman 4:22 (Book of Mormon)
The book of Helaman picks up the fictional race war between the Mormons and the people of color around 50 BC. In this verse, the Mormons became corrupted. As the people were persuading the Mormons to turn back towards good, the leaders of the land used this final excuse as a last resort. They told the Mormon people that they were wicked like the people of color.
This line of talk is all throughout the Book of Mormon, in which they claim that all people of color are wicked. This stereotype is not true.