Epson LT-286 - Manual (Page 139)

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 colors are also correct, press Y and then
Enter to end the test.
Note
On the LCD display, this test is run with gray scale mode 2 in
effect, regardless of how the DIP switches are currently set. Table
1-2, in Chapter 1, lists the mapping of colors to gray tones in
mode 2.
If any colors are displayed incorrectly, check the adjustment of your
monitor (if you are using an external monitor) and be 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 then Enter.
The screen displays three patterned squares like the ones shown
below:
D-24 Performing System Diagnostics