I think that most of us must see nebulae greenish, but as it's moslty "monochrome" we often interpret it as grey.
I always see diffuse nebulae as monochrome; except perhaps M42 which has a hint of purple / pink (faint pink actually) in the brightest area in the 16"; I've seen it reported in large scopes elsewhere. A lot of the small planetary nebulae have a blue and/or green tint.
-------------------- Matt
CI700 mount with various scopes on top.