Clarity of colour
When considering the representation of distance or depth you need to look for glass that is less pure. The colours that are muted or have a touch of white, blue or grey will provide a good representation of distance. The pure colours will appear more brilliant among the more muted colours.
This is where glass samples can be most useful. By holding them up to the light, you can see the effects one glass has on another and how one colour will appear among the others.