Like many other people have mentioned here, Jean Toomer's mixed racial background made it difficult for him to identify with either the black or white communitites, preferring instead to be called an "American". But after witnessing the segreagation in Georgia as a school principal, Toomer identified himself with the African American communites. I think this strong association with this community comes through in his poems Karintha and Fern.
In these poems, Toomer is celebrating the beauty of two black women. The description of Karintha's beauty is tied directly to her color, "Her skin is like dusk on the eastern horizon". Toomer repeats this simile comparing Karintha to dusk multiple times throughout the poem, and shows how he finds incredible beauty in her dark skin color.
In Fern, another poem about a beautiful black woman, there seems to be more of a distinction between black and white people. He points out that the white men left Fern alone. Also, the speaker of the poem shows concern that somehow Fern will end up a concubine to a white man, and that he has to do something for her to ensure nothing like this will happen. This again shows a connection and identification with the black community, fighting against the white men who were taking opportunities and other things away from them. This, along with his description of beautiful black women, shows his identification with the black community during his time in Sparta, Georgia.