But aesthetically White, when it comes to blades, makes me think of a clean/barely-used blade which still hasn't faced the issues of aging like staining/oxidation yet. It could also be a reference to the kind of material used in them. White metals usually refer to light gray colored metals and alloys like as silver, white gold, platinum, etc; which is fitting for some of those that are translated as Noble Sword in other languages right?
There's a bit of an overlapping there too as silver is usually seen as a purifying metal in folklore, so maybe it could be a bit of both.
As a quick historical fact, gilded swords are a thing.This is what my first thought was, but stated better. Similar to my theory that the magic swords are attempts to replicate the Master Sword; white swords could simply be made of silver (or silver plated), in an attempt to make weapons that are better at dispatching demons.