In light of all the recent Wuthering Heights discussion about Heathcliff's race, whether he's necessarily a man of color or might just be a dusky-skinned white man, and all the evidence that could point either way in the text, I'd like to share these comments.
When Heathcliff comes back after his three-year absence, Nelly describes his cheeks as "sallow" – a dull, sickly yellowish color.
Jane Eyre uses the exact same word to describe the complexion of Richard Mason, Bertha's brother.
I used to focus on that description of Mason as evidence that Bertha and her relatives are white Creoles (e.g. of Spanish or French descent), not part-black Creoles, and that besides ableism, the problem with Bertha's characterization is xenophobia, not racism. Charlotte Brontë called Mason's skin "sallow," not "dark."
But with the reminder that Emily Brontë used the same word to describe Heathcliff's complexion at one point, I realize it's ambiguous. On the one hand, that description might imply that Heathcliff is paler than we'd expect, and that by modern standards he might (just might) be an "ethnic white" man, not a man of color. On the other hand, the fact that an obviously POC-coded character like Heathcliff can also be described as "sallow" shows that this word doesn't necessarily mean Mason's skin is light.
Meanwhile, departing from the subject of race, rereading that scene of Heathcliff's return makes me notice its parallels with the earlier account of Hindley's return from college.
Both Heathcliff and Hindley come back after being gone for three years – the exact same amount of time – and are both greatly changed in their looks and demeanor. Both are better educated and more socially aware than they were before, both have become crueler and more ruthless, and both are ready to use the power society grants them – either through money, status, or the patriarchy – to "crush those beneath them," as Heathcliff says. And both, I now realize, are described as looking more sickly than before. Hindley more so, since Nelly describes him as thinner and paler than he used to be. But even though Heathcliff's body looks stronger and more athletic than before – which makes Nelly guess he might have been in the military – his complexion has turned sallow.
Throughout the book, sickliness is associated with over-civilization, while "robust good health" is enjoyed by simpler people attuned with the Yorkshire countryside and its culture. This is most obvious in the illnesses and premature deaths of Catherine (which happens because she betrays her true nature and becomes over-civilized), Edgar, Isabella, Linton, and Frances. But maybe it also appears in the thinness and pallor of Hindley and the sallowness of Heathcliff's face when they come home after three years of becoming more "civilized" and quickly turn to villainy.