I was trying to get a Stamp for somebody else and got the quest ‘Make two Nice Curveball Throws in a row’. I threw the first on a Sudowoodo and sadly caught it for him. Sudowoodo is pretty eady to throw Nice on. Then there was nothing to catch for like 5 minutes.
Finally a few Pokémon appeared: Some Rattata, Pidgey, a Swablu and a Illumise. I chose for the Swablu to throw a Nice at. Guess what: the Swablu was shiny😂. And indeed, the sparkles didn’t appear. I got the 2nd Nice Curveball Throw on the Shiny Swablu too.