"In earlier editions of the Book of Mormon this phrase read 'white and a delightsome people.' The manuscript that the Prophet prepared for the 1840 edition was changed to 'pure' rather than 'white.' In the theological sense the difference is slight, 'white' being the symbol of purity (see Alma 5:24; Mormon 9:6; Revelation 19:8)." (McConkie and Millet, Doctrinal Commentary on the Book of Mormon, vol. 1, p. 356)
Hugh Nibley
"White means delightsome if you consider the various meanings of white. Next he says that the Jews 'shall also become a delightsome people.' Were the Jews black? This is using white and delightsome in the broadest sense, as against the dark and uncivilized." (Teachings of the Book of Mormon, Lecture 22, p. 357-8)