You probably get this one a lot, but I've tried to research it myself but get conflicting answers. I used to be content knowing that pic related happened in a vacuum, no oxygen, hypergolic reaction, etc. I looked up some videos about hypergolic reactions and they do make flames. Then I looked up some videos debunking moon landing hoaxes and they said hypergolic reactions make "clear flames", and then show Titan II's launch stage making a "clear flame", which is nothing like the hypergolic reactions from like the Periodic Videos video on hypergolic reactions.