Freckle Juice is a 1971 children's book by Judy Blume.
More than anything in the world, Andrew wants freckles. His classmate Nicky has freckles -- they cover his face, his ears, and the whole back of his neck. (Once sitting behind him in class, Andrew counted eighty-six of them, and that was just a start!)
How Andrew finally manages to achieve a temporary set of freckles -- and then isn't sure he really wants them -- makes a warm and hilarious story.