Just for clarification, it looks from Google Earth that the overhead line he struck was a four wire, in vertical formation, 415/240V line, that runs across the southern end of the field he was landing on. (though the height quoted as 40ft is a bit high except for pylon lines, 20ft would be more accurate).
The reason for the "green wires" is the natural oxidation of copper wires, as new they would have been nice and shiny copper colour, but over the years they turn to green
Why does copper turn green?