As Ish states, the experimental earthwork on Overton Down started going green within weeks, incidentally I could be wrong but I think the EE is 50 next year !
Anyway, it was Caroline malone I think that first came out with the white Silbury business, its in that EH book on Avebury that was put to the sword by one review I recall. She is now a big noise in the British Museum.
Incidentally, some idiot at the council deciuded to remove the old sign posts at Wymans Hill (Windmill Hill) and substituted that sort of formica look-a-like signs with black etched in names for the old wooden board - within a few weeks it was green, and I passed it this morning and it had gone black.
VBB