What are they for?

Well they are minions and there is an achievement that can be gained by having every color of Snow Fairy in your inventory at once. Other than that I don't believe there is a "purpose" to them. They are just pretty. :D

The snow fairy is the hardest to get. The colored ones are all around. I didn't get one last year so I am really hoping I will be lucky this year.

Gotcha, thanks :D