This is not unusual. Perhaps the difficulties of you and the other ancestor commenters in discriminating colors (and other visual phenomena), have made you compensate by becoming better at these tasks than average (and better than the test expects you to be), maybe by recognizing and amplifying other visual cues.

There's plenty of examples of people respond to adversity/different-ability level in a domain by deliberately developing super competence. Childhood asthma sufferers who became competition swimmers, is one.