When my son was small, my father-in-law asked if he knew his colors? He did. Then dad told me there was colorblindness in the family. My husband was not colorblind.
Years passed, and my husband lost the sight in one eye. That was when we realized he was now colorblind. I asked his doctor if people can be colorblind in only one eye. He thought that is what happened. We have learned that one of my grandsons is colorblind. But that didnt keep him out of the Marines.