Eye color is more than just a single gene. Yes, most of the time brown eyes is dominant and will overpower blue eyes, but there are some genes that will cause the brown not to manifest giving a blue eyed child that carries a brown eye gene.
My wife and kids are an example of this. I have blue eyes, as do both of my parents. My wife has blue eyes. Her dad has blue eyes and mom has brown. Our three children all have different color eyes: straight brown, straight blue, and hazel.
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