I once had a nightmare that was completely in red. Like I was looking through a red filter or something. Only dream I've ever had in just one color.

I had this recurring nightmare when I was really young. I think the last time I had it I was 6. One major thing about the dream was this weird monster that had a head on each side (each head was also a leg/foot) so it would keep flipping over, but would always be upright. The other major thing in the dream was that I was being chased by a secret occult society. They would all wear this symbol. It was something like a triangle with an eye in it. So whenever I saw someone wearing that symbol I knew they were in the society and it was either time to run or try/hope not to get noticed.