Another possibility is that she's XY, but the Y never activated, so she developed female but with a single "faulty" X chromosome.

I don't remember my biology classes well enough to say, but wouldn't that also mean that potentially neither of her parents were colorblind, since the Y would've come from her father while the faulty X would've come from her mother? And, if she were XY in this scenario, wouldn't that mean that she'd pass that trait along to her kids as well?