"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.)

Yes, Creature from the Haunted Sea IS pretty goofy-- but the film is entirely tongue-in-cheek. Compare that to the Phantom Planet thing which is SUPPOSED to be scary.... arrggghh. Woof.