Yes they can in fact say this. You do realize english is not the only language that exists or ever existed right ? Or that northern american culture is not hegemonic (yet) ?

Niger/nigra/nigrum is a latin word that simply means black or dark without all the prejudice attached to it in english, and believe it or not, variations of that root word still exist in a shitload of european languages and dialects to signify the exact same thing : a color.

To claim as you do that the denigrative usage of the word is the only understanding some farmer from the depths of the Urals should have is frankly preposterous.