Hi,
The WF/Powell colour known as Santuary Blue is very similar to Barbara's vase - although on my screen her vase does not appear to be as deep a hue as that of WF.
Naturally the colour can vary, but generally speaking the WF colour is more intense than that of S&W/RB's wares.
There are a number of shapes by WF/Powell that used Sanctuary Blue, and although it is not common I would say is was scarce, rather than rare.
Nigel