What is the "Color by number" card in my coloring book?

In a Coloring Books book it only explains that color by number is a studio of its own: a number in every space, a named color key under each picture, numbers big enough to read, answers in color at the back. If you do not own Color by Number, it says "Unlock Color by Number in Activity Studio to use it ($97, one time)." If you own it, it shows the button "Make this a color by number book".