It’s a two color book (black and blue) as were many books of the period. I’m always amazed at how much illustrators of the time got out of the limited color printing. So many big books (by the likes of Dr. Seuss, Bernard Waber, Maurice Sendak among others) were published at the time with more imagination than many of the current books with full color.
The artwork, unlike his other book Piccoli, is composed of graceful and delicate line drawings with the simple, flat color. The work looks very much a part of the brilliant illustrations and art coming out of the 50s, influenced by Ben Shahn and Gregorio Prestopino.