So it turns out I'm the Goldilocks of paint, the previous sample pots I mentioned (here) weren't quite right, Sapphire Springs was very close and a really lovely blue but not quite as dark as I wanted it. However the good news is that I have actually found a paint, I know amazing right.

So the paint in question? Fired Earth's Fountains Blue

It took an extra 3 samples to get here

Described as:

A strong blue but at the same time, quiet and tranquil, like the ruins of Fountains Abbey in the twilight.

Fountains Blue definitely has a purple base colour, in fact it looked so purple when I first painted the sample I dismissed it. However once it dried it darkened down and more of the bluey tones came out.  It's not the same as Midnight, it's definitely more purple but it does have that dark night sky look I was looking for.