I remember in 1986 the Benetton team painted their tyre walls bright colours in practice. I think they did that to draw attention to them rather than make then more environmental, afterall, didnt the green dye come from some raw resource somewhere?
If they want to pretend that their tyres are green they should make them run the same set all weekend and only let them have another one when the canvas shows through.
Mind you that'd be a bit like the office stationary manager only giving out new pens if you return the old one out of ink of course, i've had a jobs worth office manager like that before so I just stole the stationary cupboard keys.