Okay yes i have evidence but just to let you know people reset for suicune entei and raikou so there shiny. Im a shiny pokemon hunter my last reset shiny was a treeko and i have lots of experience with shinys before d/p even came out.
1. My friend came across a shiny hoppip(green) in it and was able to catch it with me standing there.
2. Youtube shiny shadow pokemon(something like that) you'll find a vid of a shadow shiny sudowoodo(red bushes and yellowish body) and gives proof to it being legit.
3. Nintendo makes shinys determined by sid and other hidden values. Any pokemon that doesnt have a set sid can be shiny. All pokes in collo dont have a set sid so any poke on collo/XD can be shiny. and nintedo did make shiny collo sprites so who ever gave you that info is full of s***.