To find an answer, you would need to look for clues within the context of the story or media where Cleo appears.
For example:
* If Cleo is a character in a book: Pay attention to descriptions of her clothing, her room, or her artwork. Are there any colors that are repeatedly associated with her?
* If Cleo is a character in a TV show or movie: Observe the colors of her clothes, the background of her scenes, or any objects she interacts with.
Without further information, it's impossible to know for sure what Cleo's favorite color might be.