This photo from an ad on Craigslist shows a 3/4" thick sheet of plate glass up against a grey cinder block wall. Look how green the camera sees it as! When you take a photo in a tank like this you're essentially shooting through a green filter. Glass is green because of the mineral imputities in it, mostly iron. You can get iron free glass, but it's pricey, but it is clear. This is borosilicate glass, nor regualar glass made with iron. Borosilicate/low iron glass is not hard to find in the kitchen or lab. Lab glassware and kitchen glass measuring cups are made from this. Look down the top of a Pyrex jug, it's clear, not green like looking down the top of a Coke bottle. High iron glass is especially green, some old pop bottles are goos examples of this.
