Healthcliff simply wasn’t a mulatto despite his gypsy eyes - any more than Alexander Hamilton was. Yes, Merle Oberon seemed to be of mixed blood but that doesn’t make Heathcliff anything other than British. The Welsh often have very dark eyes as do the “black” Irish (of which my father and myself are descended from).
I wasn't saying he was mulatto, just that in the novel he is described as being dark, like a gypsy. I am not familiar with the version the OP was talking about but think I found it and it looks simply awful, truly awful, and not just because the actor who plays Heathcliff is black.
http://www.imdb.com/title/tt1181614/videoplayer/vi4277052441?ref_=tt_ov_vi
Again, I liked the 1939 version but also the 1992 version.