I do not have any Pied animals but I have a SuperFire, a Hypo Lesser/Mojave and I had an Ivory Butter OD Pastel so I know a bit about white snakes. I have also visited a number of friend's collections and seen adults of a bunch of things.
The most stark white snakes I have seen are the all-white BlkELs. The white I have seen on adult high-percentage Pied animals is the same degree of stark white so I would believe that an all-white Pied combo would be equal in that regard.
Every BluEL adult I have seen has had some faint level of pigmentation to them, they are more cream-coloured than white. I have also yet to see an adult BluEL of any type that does not have some kind of faintly visible dorsal stripe