CiM Prussian Blue is an opaque, dark steel blue. When it is hot - it goes blue and green, and looks very much like Class M Planet.
Once out of the kiln though - the colours are more of a blue and a steel grey, darker than Class M Planet. Interestingly, the final brush with the flame across the glass brings up a colour that is more like a periwinkle, before it goes in the kiln - but there is no sign of that after it comes out. That actually seems to be where the bulk of the steel grey is after - so some experimenting with heating would be in order, I think.
Interesting. Not sure what to do with it yet.