It is quite clear that race is central to this excellent short story, due to the contemporary belief that whiteness is superior to blackness. The story is built around Armand and his belief in his own natural superiority because of his whiteness. His genetic dominance is stressed through his belonging to "the oldest and proudest" family in Louisiana. It is because of this presumably secure background that Armand naturally believes that his child's mixed ancestry is thanks to the unknown Desiree, who has an "obscure origin." When Desiree herself becomes aware of the coloured skin of her baby, note how she reacts:
The blood turned like ice in her veins, and a clammy moisture gathered upon her face.
Although this does not cause her to abandon the child, the way that Armand is so swift to abandon his wife and babe, the shock of this new reality and the consequences of what it would mean is enough to force her to commit suicide and to ensure the death of her child.
The irony of the discovery of Armand's mother's letter at the end that shows it is him who is responsible for the coloured nature of his child thus comes to late in a story where race and the colour of skin is everything. His cruel rejection of his wife and child because of their lack of whiteness comes back to haunt him.