right, I've also had a good look at my fish again today and this evening.
And what I'm pretty sure of is that the neck and button rim and the v shaped bit that goes down into the vase is some kind of different blue to the wings - not the same as the turquoise blue on my inkwell that has a polished pontil mark, and not exactly the same as the Czech turquoise bowl either (my camera picks that up as turquoise but not the mdina fish as turquoise and the fish isn't the same degree of turquoise as the bowl), but it's also not cobalt blue as far as I can tell.
However my vase also has the neck cased so the best place to show the different colour of the blue is at the low point of the v where it joins the cross of the wings as it were. In the first photo that point is where it looks the brightest clearest palest blue if you can see that?
However, what I can say is that the wings of my fish have cobalt blue swirls in them. And looking at it with fresh eyes, that is probably why I asked when I first bought it, if it was a cobalt fish vase
I only had camera back from son this evening so I've had to take pics under artificial light - I don't know if these will work but I will try again in daylight tomorrow and add some more.
My comparison is to a G Elliot vase that has a slightly purply cobalt neck, I think it's slightly purply and not quite exactly cobalt to be honest, but it's near as dammit to the cobalt sidestripe and it shows the comparison better because it's a little more transparent than the sidestripe.
On that photo you should be able to see the cobalt streaks in the wing of the fish vase as a comparison.