I used to believe that duck eggs had a blue yolk inside, before realising that it was just the shell. At least that would be more unique than just yellow ones.
A childhood belief about birds

others believed things like this
- I used to think that the Cadbury eggs, that come out at Easter, were filled with real egg yolk.— d
- I used to believe that the sky is just a very thin blue egg shell— Alan
- I didn't understand about boiled eggs until my Mum explained I wasn't supposed to eat the shell as well.— Chris
- I used to think that eggs were made in a factory. The oval shell made them fit perfectly in the egg cartons.— Sherry
- i thought that "aromatic" duck was actually "asthmatic" duck.
poor thing...— rachael - I always thought that duck sauce (from chinese restaurants) was duck poop.
— emily