Jack Nicklaus has been color blind his entire life. The effects were so severe that he couldn't even distinguish between the different colored numbers on leader boards while he was competing. According to a story from Sports Illustrated:
At the 18th green, I looked at the leaderboard, and I saw several 1s and 2s. I'm color-blind, so I said to my caddie, Willie Peterson, 'How many of those numbers are red?' He said, 'Just you, boss.'"
Jack is what's known as Red-Green color blind, which means he can't distinguish between the two colors. When he sees them -- especially together, they kind of blend together into a kind of brown.
Having a hard time imagining what that would be like? Well, Buzzfeed put together a good video that describes what it's like: