Ted Newsom wrote:
"Blue screen": yes, in theory you can use any color. The old Rank/Disney "sodium" process used yellow, to a much more exactly effect than any blue screen work over the years (but they screwed up the special prismic lenses & no one ever made any more.)


Disney had the rights tied down and were the only ones legally allowed to use the sodium technology in North America... Which is why Harryhausen had to go overseas when he wanted to use it.

I'd heard from one of the old guys in the optical department over at Disney that the company only owned two sodium optical printers and one of them had a lens with defects.  That left them with only one of them that they could count on for over a decade.  The Disney company babied their one good optical printer for years, even cannibalizing parts from the other one to keep it going,  Finally it just became too financially stressful putting all their eggs in one basket and they said "Aw, the hell with it!" and moved on to other technology.  ...Or so the story goes as he told it.