Nephi appears to be describing a skin color and attaching positive value to whiteness. “White, and exceedingly fair and beautiful” certainly all sound like references to physical appearance. Nevertheless, this verse is still best read with the white/dark dichotomy referring to righteousness rather than skin color. (See commentary accompanying 2 Nephi 5:21.)
“White” and “beautiful,” I argue, are best read as receptiveness to God. This verse acts as an introduction to the next important aspect of the invaders—that through them, the gospel would be returned to the Lehite descendants. The “whiteness” of the gentiles is required of their structural position contra the “dark” Lamanites to whom they will bring the gospel. (See commentary accompanying 2 Nephi 5:21 for an expanded discussion of the color and skin issue in the Book of Mormon.)