Colorblind people may be missing one of bladder cancer’s most important early warning signs: blood in the urine. Credit: Shutterstock Seeing blood in urine is often the first clue that something is wrong. For many people, noticing this symptom prompts a medical visit that can lead to an early diagnosis of bladder cancer. However, for people with colorblindness, detecting that warning sign may be far more difficult. Because many forms of color vision deficiency make it hard to perceive red tones,