I can never trust shop display models to be a fair comparison of the display image the unit is capable of, so don't read much into the display image.
As you say the image depends on the source, and the colour settings on the TV. Make sure you are able to adjust sharpness, colour, contrast etc. so that you understand what the TV is capable of, its an age old trick to have the contrast levels of TVs adjusted differently to make one look better than the other.
Only trust the image if you know the source is as good as the one you going to be using at home and you have complete control over the settings of the set.