A friend of mine is a private pilot and red/green color blind. Technically, color-blind people are not allowed even to get a private pilot's license in the US. However, he was able to distinguish red and green runway maker lights and so was deemed not technically color blind.

It took some practice for him to be able to do so. Most green lights for applications like traffic lights or runway lights are made with some blue in them to help color blind people distinguish them from red. This was enough for him to get his license.