Davie:
According to "The Evolution of Instrument Flying In The U.S. Army" by Maj. David M. McIntosh:
"Every pilot had to be certified instrument qualified once per year. The certification process was more complex than the simple check rides required previously. It included
a twelve-hour flying training course; a written examination; and a check flight covering basic maneuvers, navigation procedures, and instrument approaches. There were two types, or levels, of instrument certification: Form 8 (White) for less experienced flyers and Form 8 (Green) for the more experienced. "Green card" pilots had fewer restrictions and could fly in worse weather than "white card" pilots. In order to qualify for a green card, pilots had to have a minimum of one hundred hours of actual (not hooded) instrument time. Green card holders also had to take a more demanding check ride than white card holders. The two-tier certification was probably necessary because of the wide diversity of instrument experience among AAF pilots."