It's super easy for people to not know themselves of being color blind, since it's been that way for them since birth they don't know any different.... However, they normally pick up that a kid is colorblind or not when learning colors.. Also, it's technically not completely impossible for her to still become an astronaut being colorblind, as it depends on the type of colorblind she has. Since their are many types of colorblindness, I'm pretty sure that as long as she falls in the category that is shown to be similar to "minor" colorblindness, that if she was a step above from everyone else, she could still be one. However, it would be insanely difficult, since that alone will always be in the back on their minds when selected people.