60th anniversary edition front book cover for Harold and the Purple Crayon. It's very purple, in contrast to the book. which only uses vibrant purple for the things that Harold draws agains a white background.

Harold and the Purple Crayon by Crockett Johnson (Harper & Brothers, 1950).

I introduced this book to my granddaughter yesterday (via video chat), and she adores it. Apparently it once made an impression on my son, too, because he said it had been his favorite. It's a simple story in which Harold takes a walk, creating the world as he goes with a big purple crayon.