The whole problem of "what is a negro" is unfortunately one that the LDS church inherited from Brigham Young's era.
For what it's worth, here's how it was defined scientifically back in the day (starting about halfway down the page):
http://books.google.com/books?id=w1cSAAAAYAAJ&pg=PA467&output=html
Robley Dunglison was a prominent author of medical books, and he's basing the definition on Cuvier there, so that's a pretty mainstream summary for the mid 19th century.
Brace yourself, because the racism is pretty bad, but you can see even then they were struggling with the cognitive dissonance of what was obviously true compared to what they wanted to believe: "This case of great intelligence in the negro is not unique; and it exhibits what may be expected from him under favourable circumstances. In almost all situations in which he is found, it is in the state of slavery, and degradation, and no inference can be deduced regarding his original... intellectual capability under such circumstances.... It must be admitted, however, that from organization, this race would seem to be,
caeteris paribus, less fitted for intellectual distinction than the Caucasian."
For what it's worth, the representative "negro" pictured there is from this painting (reversed because the engraver just drew it as he saw it):
http://en.wikipedia.org/wiki/File:Jacobus_Capitein.jpg
The problem is, as we now realize, that scientific-type people were picturing the "negro" as a pure archetype which became mixed as it blended with other pure archetypes like the "caucasian." So in places where dissimilar people mated, the darker skinned offspring weren't "negroes" anymore
scientifically (by the science of the day), but white people still wanted them to be, socially and legally.
The same book goes over the issue of mixed-race people here (toward the bottom of the page):
http://books.google.com/books?id=w1cSAAAAYAAJ&pg=PA308&output=html
So you had scientific definitions, legal definitions, and social definitions--all in conflict.
And that's why I (and probably most others here) predict that Janadele and the LDS church can never get beyond a definition that basically amounts to "We know 'em when we see 'em--you know, those kind of people."