Like most of the people here, I didn't know about shiny pokemon when I first saw my shiny.
I remember it was in Pokemon Silver (the original version) and I was on my way to the cave to go to Azalea Town and I saw an Ekans!
I didn't know it was shiny because, to me, the color looked the same and I thought it was the lighting around my house when I was playing.
I ended up killing/fainting it and my Totodile evolved :\