It involved the tower shining lights at him and as long as he could tell the meaning of the lights, a certificate was issued.
The FAA official would have issued a SODA - Statement of Demonstrated Ability. You take it with you to your medical and the doctor will ignore the problems the SODA covers.
Deaf, one eyed, paralysed from the waist down, and colour blind people are happily and safely flying in the US - but this guy is in the UK. Best bet for bd01uk is for the CAA/JAA to be dragged into the 21st century and introduce sensible and reasonable medical standards. It may be hard to believe, but there is more chance of that happening soon than a cure for colour blindness.