I have photos of all the artwork before the painting went ahead.
Over the 15-20 years it was there, it had not lasted well and it was time for a change. It is not impossible for space to be made available for graffiti art in the subway but the paint work was one of the few bits done in a hurry (no idea why, but it did take months to stop running).
Offered the choice of white or grey or purple or orange, a few of us reached a consensus that Green was the right colour for the Forest Hill subway. You'll notice roughly the same colour is used at the Dartmouth Arms, on the background of this website, the Forest Hill Society website, and Southern Trains. (I would have gone for a slightly lighter shade of green, but I don't feel the shade used is too oppressive).
I would be interested in other suggestions for the subway colour scheme, in case a chance comes along again. Is there a colour that is more acceptable than 'industrial strength vile green'?