Snow white is a pure brilliant white. Snow white linen, a snow white beard, washed snow white.
Snow looks that white because it is full of air and scatters every wavelength equally. As a comparison it is very old and appears in English long before the fairy tale.
1adjectivesnow whiteA pure brilliant white.
“He came down in a snow white shirt and no tie.”
snow white is a colour.
Proto-Germanic
*snaiwahwītaz
Proto-West Germanic
*snaiwhwīt
Old English
snāwhwīt
Middle English
snow whit
English
snow-white
English, today
snow white
snow-white comes from Middle English snow whit, snowe-white, snouwite, snawhwit, from Old English snāwhwīt, from Proto-West Germanic snaiwhwīt, from Proto-Germanic snaiwahwītaz; equivalent to snow + white. Cognate with Dutch sneeuwwit (“snow-white”), German schneeweiß (“snow-white”), Swedish snövit (“snow-white”).
Etymology from Wiktionary, CC BY-SA
Practised in Colours & Patterns