I would do this one of two ways. First, undercoat in a light colour and then carefully shadow it - don't be temped to go too dark anywhere - before layering on straight white for the highlights. Second, undercoat the entire thing in pure white, then shade carefully.
With true whites I think it's generally best to strive for neutral-grey shadowing, but taste prevails here and if you want to go brownish (i.e. something like beige) or blueish then that can work too. Just need to be careful to keep enough white showing so that it's clear that the item is white, not brown or blue with extreme highlights (kinda like leaving enough black on black items, so that it 'reads' as black and not the highlight colours with dark shading).
Einion