Mine was a shiny Teddiursa in Silver, but I didn't realise it was shiny until it was around level 50 since I had no idea what shiny Pokémon were back then and I only caught the Teddiursa because I really wanted to use one on my team. It's just lucky that it was something I wanted to catch that came up as a shiny, otherwise I would've most likely killed it. Looking back, I'm not sure how I didn't notice it was green paha.