Scribble by Deborah Freedman is about a pair of sisters and their drawings. The older sister loves to draw princesses and has a very set opinion on how drawings should be done. The younger sister prefers cats and is a little freer with how she draws — basically she scribbles.
But it's through the drawings that we get to know the girls. See the cat and the princess form a friendship across their papers and together they make something useful of the left behind scribble.
This book reminded me of Picture Purrfect Kittens by Erika Tatihara and Masuru Misobuti but with an artistic style that's similar to Crocket Johnson's Harold and the Purple Crayon books.