What colour(s) is a prophecy?

Argh, I hate it when I log on and realise I've not written anything for over a month! In that time I've applied for several jobs, been in a recording session for BBC Radio, seen Equus, and seen The Dumb Waiter (and Jason) again. More of that later, but meanwhile, a poll (with grateful thanks to annephoenix, who generously gifted me 6 months of poll-making ability last December. Though I've not exactly made full use of it, knowing I've had the option has been wonderful!)

[Poll #954377]


(By which I mean, lest it needs defining, those spheres in the Department of Mysteries. I had thought they had a canonical colour, but can't find a reference to it.)

(And of course now someone is bound to make me feel stupid by pointing to a definitive canon reference, but at least that will have answered the question...)