i think white pens go best with brighter blue inks or even the subtleness of grey inks. perhaps Noodler's Ottoman Azure Blue? or maybe Diamine Grey?
I unfortunately struggle writing with grey (including pencil) because of my colour-confusion issues: they all look very, very faint to me.
Momiji cleans out easily and is quite pretty.
I have a sample of Momji in my ink box so I might load up the converter when the Waterman's I-Don't-Know-Which-It-Is Blue cartridge runs out