Epson 10020 - Manual (Page 175)

The same pattern is displayed again; this time the squares are
cyan, white, and magenta, and the background is red. These
colors are called Color Set 1. If these are also correct, press Y
and then Enter to end the test.
If any colors are displayed incorrectly, check the adjustment of
your monitor and make sure that both ends of the cable are
plugged in firmly. If a problem still exists, press N and Enter to
display the error message.
640x200 Graphics Mode Check
To check your 640x200 graphics mode, press 6 and Enter. The
screen displays three patterned squares against a black
background, as shown below.
If the patterns on your screen are clear and distinct, press Y and
then Enter.
D-18 Performing System Diagnostics