Ethna [not Ethina] Carberry's poem cited by Mark Urquhart sounds most intriguing. "The Four Winds of Eirinn" can be viewed online. I wouldn't say that the lad addressed in the poem is definitely dark-skinned as well as dark-haired, though perhaps the "mouth of white pearls" suggests his teeth contrast with his skin colour:

My Black Slender Boy, you have nothing but health–
Yet your diamonds of eyes are far rarer than wealth;
Your mouth of white pearls, and your locks of the jet
Would buy all my fortune and leave me in debt.

The hate and scorn of the narrator's parents towards the Black Slender Boy may be because he is poor and they are well-off, rather than because of his colouring.

My Black Slender Boy, though my father may frown,
And my proud mother pass you with scorn in the town,
While they bargain at making a match for me there,
With Red Ulic Keown in the heat of the fair–

note that Ulic[k] would have red hair, not red skin ... and that would be a typical way to describe someone in Irish language (Úna Bhán, Uilleac Rua, Domhnall Dubh - fair haired, red haired, black haired)

https://digital.library.upenn.edu/women/carbery/eirinn/eirinn.html