In response to two NTSB safety recommendations, the FAA stated that it has only identified three accidents involving pilots with valid medical qualifications in which color vision deficiency (CVD) was cited as a contributing cause.
As you mention above, on July 26, 2002, a Federal Express Boeing 727-200F crashed during a visual approach to Tallahassee Regional Airport in nighttime visual meteorological conditions. The three crew members were seriously injured and the airplane was destroyed in the crash, which the NTSB attributed to “the captain’s and first officer’s failure to establish and maintain a proper glide path.” Because the first officer was flying the plane at the time of the crash, the NTSB cited as one of several contributing factors “the first officer’s color vision deficiency" which interfered with his ability to discern the red and white lights of the precision approach path indicator (PAPI).
On Aug. 29, 1992, an incident occurred in which the pilot of a Mooney 20F with “a waiver for partial color blindness to red and green” landed on a closed runway that was marked with orange crosses in the dirt 50 ft beyond each end. The pilot’s “limited ability to detect the orange-colored marking” was cited as a contributing factor.
One incident involved a Navy F4J lost on Aug. 5, 1980, “when a severely color deficient pilot failed to interpret correctly the colored navigation lights of other aircraft in the area, leading to the false impression of a collision.”
Regarding the severity of the FO's color blindness from FedEx flight 1478, records indicate that he passed all color vision tests during his 16 years as a U.S. Navy pilot but failed a test administered during an FAA medical evaluation in 1995. This failed test indicated that he had a mild red-green deficiency. The FAA issued a first-class medical certificate with a statement of demonstrated ability (SODA), based on his years as a Navy pilot and the results of his Navy color vision tests. He was issued this SODA on all subsequent medical examinations.
After the 2002 crash, the first officer passed the Farnsworth Lantern (FALANT) color vision test, which was designed to differentiate between those with mild red-green deficiencies, who pass the test, and others with more significant red-green deficiencies, who fail. He also passed a light-gun-signal test administered by an FAA medical examiner. However, he failed seven other red-green color vision tests and was determined to have a “severe congenital deuteranomaly” — a red-green deficiency that is the most common color vision defect.
Hope this helps.
References: Werfelman, L. (2008, December). Color deficient?[PDF] Aero Safety World, 38-41. Flight Safety Foundation. Retrieved from:http://www.flightsafety.org/asw/dec08/asw_dec08_p38-41.pdf