You’ve caught a Shiny Pokemon!
Previously formally often known as alternate coloration or uncommon coloration… [a Shiny Pokemon] is a selected Pokémon with totally different coloration to what’s ordinary for its species. It is among the many variations Pokémon can have inside its species.
They are usually fairly uncommon, and the sport will warn you for those who attempt to switch them.
Should I evolve it or not? Will it lose its particular eyes?
Shiny Pokemon will stay shiny after evolution, although it is price noting that Lairon and Aggron have barely totally different Shiny colourations. The eyes will stay purple, but in addition you will discover a extra steel-blue slightly than charcoal/darkish gray underbelly.
Will it assist in any means or is it simply kinda for appears?
Just for appears, and bragging rights. Shiny Pokemon are no higher or worse than their non-shiny counterparts, stat-wise.
You can learn extra about Shiny Pokemon on the Pokemon Go Wiki