It looks more like glass than a diamond. It seems to sparkle in some parts more than others. But assuming you're looking at the diamond in a jewelry store, it should be nice and clean. The light can't get through the diamond and come back out of it. That's why its a good idea to clean your own diamonds fairly often.
Color is the most important factor contributing to a diamonds value.
The color grading scale developed by Gemological Institute of America is the most widely accepted in the world. It uses alphabet letters to indicate color. As a diamond's tint increases it's value decreases. Therefore color grading is done face down in a white card or tray. For proper illumination a color corrected fluorescent light free of ultraviolet rays should be used.