re: Question
The Horseshoe Crab has blue blood, as it uses copper rather than iron as the base of its system.
Actually, I've also read that the Horseshoe Crab's blood turns to an almost deep purple when explosed to oxygen or when it's on land.
I also tend to agree with you as far as a nebula is concerned, but no one one has yet to have traveled with it/gas or have met it to verify. The gas I'm mostly concerned with here is of course, oxygen which IS prevelant on the outskirts of nebulas.