I tried this test a while back, struggled with it for maybe twenty minutes or so, and scored something in the mid 200s I think. So I learned that I have defective color vision, which I have known for fifty years.
The very simple and straight-forward Ishihara color tests can tell you that in an instant (typically, a field of colored spots is shown, and a person with normal color vision sees a letter, while one with defective color vision may see a number or a different letter.