The strip shows a range of greys from pure black to pure white. You should be able to see a clear difference between each shade of grey, ranging from pure black (left) and pure white (right).

Along the top of the strips are alternate patches of black and dark grey. If it looks solid black to you (look very carefully), your monitor's brightness setting is too low. Increase it until you can -just- perceive the difference between the grey and the black squares.
Pass this along in your journals, it will help new and old deviants view your work as it should be seen!