As many have already pointed out here in this blog, Toomer had the ability to pass as white or black. As an obvious consequence, he did not identify or define himself by race, and, at least early in his adult life, he strove to live as a member of what he called the "American" race.
Even though there are clear differences between Toomer and Karintha (i.e. their gender, location, etc), I nonetheless see a possible allusion to his own life which comes out of the refrain: "Her skin is like dusk,/O cant you see it,/ Her skin is like dusk,/ When the sun goes down." (4) Like dusk, Toomer's race was unclear and hazy. One couldn't just "see" Toomer and immediately deduce whether he was white or black. Perhaps this is all a stretch, but I do feel there is some connection between the lack of clarity and haziness which accompanies a dusky early evening and the inability to accurately categorize Toomer by race.