I was trading someone and I put on an egg and they gave me a LEGENDARY. I noticed that it had the sort of gleam that baloons have when light shines on them and the next one didnt. I might have imagined that, but still.....Are there any eggs that look different? Was that a shiny or something? I remember it was a rare legendary . WHY WOULD THEY DO THAT?
You were probably just imagining it.
Pokemon eggs do not have a gleam on it and no eggs look different from other eggs. If eggs looked different when a shiny was in them people would have started using that for the Masuda Method.
Hope I helped!
If a legendary hatched from it, the the egg was hacked, but there is no visual difference between eggs. The only egg that is aesthetically different is the Manaphy egg, which is unobtainable as of now.