Absolutely! Though I grew up in Italy, totally missing the paint by number phenomenon, I've heard about it and I've seen some wonderful examples of paintings completed that way.
Color-by-number images are created by very talented artists that apply complex color theory and excellent shape simplification.
While you paint, observe how the colors interrelate and bounce off each other. Each color-shape does not make any sense individually, but when you put them all together they make believable and charming images.
Analyze the subject and observe the areas of color. Why did the artist design it that way? Why did he/she choose those specific colors?
I think this can be extremely useful for a beginner to move to the next step: develop those color shapes yourself.