The birds are blue.
At the start of the film, these bluebirds first appear when waking Cinderella up, bathing her, and getting her dressed for the day. They also help to fix a ball gown for Cinderella with help from the mice. Near the end of the film, when Lucifer has trapped Gus and a key to Cinderella's room (stolen from Lady Tremaine with Jaq) in a bowl, the birds attack Lucifer by dropping cups and plates on him, but the cat shoos them off. Then, Cinderella instructs them to get Bruno. They fly down to the shed to wake up the dog. The birds help Bruno into the chateau so the dog can chase and frighten Lucifer away.
The birds help the Fairy Godmother and the mice to create a book of stories for Cinderella. They also have a role in the short "An Uncommon Romance," in which, under Cinderella's instructions, they steal Anastasia's hat and get her to chase them in an attempt to bring her together with the Baker.
Only two of the Bluebirds appear in the film, where they assist Jaq and Gus on helping Cinderella's quest to regain Prince Charming's memories of her. They are the ones to lead Prince Charming to Cinderella.
As seen in one of the film's official trailers, the birds are set to appear in the upcoming adaptation of the original, 1950 classic, reprising their roles as one of Cinderella's animal friends.