Which Witch is Which by Pat Hutchins, 1989.

This is a cute picture book/puzzle book.  A pair of twins, Ella and Emily, are invited to a friend’s costume party, but they come dressed as witches in identical (or nearly identical) costumes.  Throughout the party, as the girls play party games, eat the party snacks, and give presents to their host, readers are invited to figure out which twin is which.

The main clue to the girls’ identities is that Ella’s favorite color is pink while Emily prefers the color blue.  Things that the girls have in those colors or objects that they select give away their identities

However, there are also other hints, like we are told what each of the girls ate at the party so that we can use the crumbs left on their plates (or the lack of crumbs) to determine which witch is which.

The text of the book rhymes.  The illustrations are cute, and it’s a good book for teaching children how to notice details.

The book is available to borrow and read for free online through Internet Archive.