How is the FM5 256 color palette organized?

[Moon]

I have been trying to decypher the system by which the FM5 256 color palette is organized without much success. Colors seem to be lumped in bunches without any order, except for the gray scale. Has anybody cracked it, or know of where it is documented? I have determined that colors along a horizontal row seem to go together nicely, but other than that, I am puzzled by how to locate that one right color easily.