Why would we do this? Shininess is impactful for information about different Pokemon sets (e.g. a shiny Greninja can't have Battle Bond, and only a shiny Genesect can have Shift Gear). You can't turn off Shininess in-game. Plus, Shiny Pokemon often look cool! The number of people who would utilize this option would be very low, and I can't think of any positive reason to implement it.