That's not true for every test, the one I just used begins with no line and then a line appears. So you don't need color vision. You do still need vision, but it's hard to use a COVID test otherwise.
Sure, but the parent specifically referenced the Abbott test. And the Abbott test instructions tell you to discard and not use the test if the blue line is not present.
See pages 6 and 7: https://www.fda.gov/media/141570/download