IBM RT PC Problem Determination Manual page 159

I B M 5081 C o l o r G r a p h i c s D i s p l a y T e s t P a t t e r n s
Test Pattern 1
The color bar pattern used on a color display requires at least four
video pixel planes. Left to right, the color bars are green, yellow,
red, magenta, blue, cyan, black, and white.
Compare each color on your screen, as described above. If any
color is missing, you have a megapel graphics display problem.
Appendix A. Locations and Examples A-9