IBM 6151 Maintenance And Service Manual page 694

Flat Field Test Patterns
The following types of Flat Field Test Patterns are available using
the Display Test procedure:
White Flat Field The red, blue, and green colors are at their full
intensity to check color purity.
Black Flat Field All colors are off.
Red Flat Field The red color is on at full intensity.
Green Flat Field The green color is on at full intensity.
Blue Flat Field The blue color is on at full intensity.
AJZB217
11-152-4 Service Manual