Regarding 2 Nephi 30:6, this article notes:
The Prophet Joseph Smith made an important textual emendation to this passage in the 1840 edition of the Book of Mormon, where the phrase “a white and a delightsome people” was changed to “a pure and a delightsome people.” According to Royal Skousen, “The 1840 change of white to pure seems to be a conscious one and was probably made by Joseph Smith as part of his editing of the 1840 edition. The change does not appear to be an accidental error based on any visual or phonetic resemblance between the two words.”
… and the article also notes:
Why might Joseph Smith have made this textual change in 2 Nephi 30? Skousen elaborated that “the editing change to pure may represent a conscious attempt at avoiding what was perceived as a difficult reading (the Nephites were supposed to be light skinned), which therefore explains why the change from white to pure was made here—and only here—in 2 Nephi 30:6.”9 In other words, Joseph Smith may very well have recognized the possible racial undertones in this passage if interpreted that way and ultimately wished to avoid them.
While it is certainly possible that this change reflected the racial attitudes of early members of the Church, who assumed many of the views of their 19th century environment,10 Tvedtnes argued convincingly that the change may have occurred to emphasize that the text is speaking of a spiritual, not biological, condition.
See the link for the full article. This photo in the article of people dressed in robes for baptisms conveys the spiritual meaning of purity and the visual white of the clothing along with the warmth and vibrancy of faces in different shades of brown.