A chance to talk to FlatpanelsHD's reviewers.
The graph says this:

The number on the left is the delta value. Delta is a difference between two factors; here it’s the difference between the measured colour on the panel and the actual colour that is our target.

# A delta value lower that 2 results in a visible deviation from the actual colour.
# A delta value over 4 or 5 results in wrong colours.
# A delta value between 1 and 2 results in precise but not perfect colours.
# A delta value lower than one results in almost perfect colours. The target is 0.
# Everything between 0 and 1 is barely visible to the human eye.
Ok, so the higher those color bars, the worse the picture accuracy? But I have seen reviews that say X monitor has good picture, that seem to have color bars higher then those that it says didn't have such good quality picture. And I can't make much sense of what the graph is suppose to say? Where do I want those two or 3 lines? What do those numbers in the lower left hand corner mean?
Ok, so the higher those color bars, the worse the picture accuracy
Yes, exactly.

But good picture quality is also dependent on factors such as gamma and color temperature. Basically you can say that color accuracy is a combination of different factors but the graph shows a measurement of a selection of (popular) colors, which also means that it's an easily read graph but not a complete one. A complete graph report takes every single step in each primary color (red, green and blue) and secondary color into account but we feel that we want a simple yet correct reporting system instead of a too advanced reporting system that only very few users understand.

The numbers in the left corner are:
- Gamma is a technical term describing “luminance”. For a complete explanation I suggest you check Wikipedia – it’s too comprehensive to cover here. We are aiming for a 2.2 gamma and TV and monitor manufacturers should do the same. The number you see in the graph is an average value but actually gamma is the complete range of light from zero to maximum light.

- Kelvin is the color temperature that describes the temperature of colors. A high color temperature means that a picture is cold and bluish and a low color temperature means that a picture is warm and reddish. We are aiming for a 6500 Kelvin color temperature and TV and monitor manufactures should do the same. Again; what you see in the graph is an average and color temperature can be measured in both dark and bright colors.

- Cd/m2 is brightness of the white (maximum brightness). The higher the brightness, the brighter pictures. For very bright rooms you should prefer a high brightness value and for dark rooms you should aim for a 100-140 cd/m2 brightness value.

But you also have to remember that picture quality is more than color accuracy. Color accuracy is important, but detailing, response time etc. are also important factors.