There are six extra squares in the lower right corner.
If you are running in "thousands of colors" mode, you may only see four.
In 256 color mode, they should all be there.
These tiles have brightness values of 1, 2, 4, 8, 16, and 32 (out of 255 max).
Adjust the monitor brightness (black level) so that the dimmest one is just visible.
Then adjust the Contrast (intensity) for your environment.
Repeat if necessary since the controls on many monitors interact.
Maximize the page and click on the color bars for a full screen image. --