Is she my sister or not?

Can a blue eyed father and hazel eyed mother produce children with four different eye colours? I have for years thought my “ sister “ is not a full sibling. My eldest brother has green eyes, I and another brother have blue. And a third brother has hazel then along comes the sister with dark almost black eyes plus slightly darker skin tone and very wavy dark hair when the rest of us are fairer with straight hair. One of my first memories is my mother telling every visitor “ you wouldn’t think they were sisters would you” ( my hair was platinum blonde until I was about five ), almost as if she were preempting awkward questions. My family are estranged so I can’t really talk to anyone about this. Please tell me what you think.