The thematic link you can make between these two texts relates to both prejudice and self-loathing. It is clear that Tom, because of his status as not being white, is the focus of immense prejudice and hatred in the town. Even though the evidence suggesting that he killed a white man is tenuous at best, it is clear that he will be found guilty for the murder and will hang because of the colour of his skin. In the same way, Armand casts out his child and his wife because of the colour of his child's skin. Not being white in itself seems to be presented as being a crime.
However, there is another, more disturbing link, and this is the way that Tom is full of self-loathing because of his mulatto status. He at one point complains that the Sherriff gave him a "black mother," and is unable to accept himself as a product of a mixed relationship. In the same way, Armand finds it impossible to even suspect that his child's dark skin might have emerged from his own racial roots and automatically assumes that it is the fault of his baby. The issue of being mixed race is shown to throw up a whole gamut of issues, and one of the most important is the way that characters find it very difficult to reconcile their status with who they are.