Poseidon, or Poseidan, as I keep misspelling it, so if I throw that in there, I'll find it next time I search - anyway - CiM Poseidon is a translucent sky blue that I reviewed a while back. It is a lovely colour, and I'm not clear why I didn't buy a bunch of it then. Probably something to do with having enough glass to start a small store, but that's another story.
I had heard that there seemed to be a colour difference between the old batch of Poseidon and the new, so armed with a rod of the old and a rod of the new, I sat down to test this out. Visually - the rods seem pretty similar, the older rod "O" on the top (fatter rod) and the newer on the bottom - "N." Held up to the light - the older rod is denser, but doh, it's thicker.
But when worked up into a bead - the older rod, on the left, actually does come out slightly more opaque.
From the left, base of Poseidon with ivory dots, and two self-coloured beads.
So - in conclusion - pretty colour - and the old and the new are functionally the same (as to be expected from CiM.) Slight variations probably come from technique. That's why we call it art. ;-)