It's probably because in real life Ramesses II had red hair, and a lot of white people seem to have a hard time imagining someone with natural red hair having dark skin and eyes, even though that was sort of a big deal for Egyptians at the time.
That being said, fair skin and light coloured eyes are not an entirely uncommon trait for the area (North Africa and West Asia, Egypt's sphere of influence at the time). Not likely they were traits possessed by Ramesses, though a very questionable race science examination tried to assert he was a fair-skinned man of Amazigh (Berber) descent in the 70s, which is probably where they drew this idea of him from. Though they nailed his big beautiful nose.
Edit: On further inspection it sort of looks like they just made a beefier blue-eyed version of Yul Brynner from the Ten Commandments