Saw this fish in mid-June off Santa Rosa Wall in Cozumel, at about 50'. As the photo sort of shows, it was in a patch of 'weed' in a large sandy area, between reefs. My initial thinking was that it is a pipefish, but it did not move like any pipefish I've ever seen -- very fast and flexible, much more like a snake. My 26 year old son, with much better eyes than mine also claims to have seen a large translucent dorsal fin, but that is not visible to me in the picture. The latter two observations make me think it could be a female pikeblenny, but I've never seen one before, so I have no comparison basis other than "the bible," i.e. Reef Fish.
The bands on the fish really are greenish, though a deeper green in the photo than in real life.