There seem to be unusual colours in this one too.
Look around the base coloured part, where there is an odd shade of blue streaking through some yellow. It shows up in your first two pics. It's not cobalt, it's duller and greyer than that, but it's not teal either.
There is some of that exact blue in my tiny MH Fish, which was dated '68 by both Tim and Elizabeth Harris.
But it would depend if that colour is exact in the photo. I've just looked at photos of the tiny fish and the colour doesn't show up correctly.
The iridesence you describe is a deposit of silver ions onto the surface, they escape from inside the glass as it is manipulated to allow that to happen.
It was originally a mistake, but a serendipitous one they tried to repeat when possible, although it's dangerous.
Breathing in that sort of substance as a gas is no good for anybody's health.