You'll need to gather all the info from the villagers and figure them out, here's the right order:
- Cow: yellow shell
- Pig: blue shell
- Chicken: red shell
- Sheep: green
- Goat: white
About this one, I asked my team—it might be a bug.
But in the version we're currently optimizing and fixing, we've added a feature that lets you take the shell back if you give it to the wrong person.
We might upload it tomorrow :D You can also check if it's already available in the current version!