Colorblindness may be doing more than making traffic lights confusing — it could also be hiding a life-threatening warning sign. Researchers analyzing millions of medical records found that people with bladder cancer who are also colorblind have a 52% higher mortality rate over 20 years compared to those with normal vision. The likely reason: many people with color vision deficiency struggle to see red, making it harder to notice blood in urine, the most common early sign of bladder cancer.