In the diagrams, a class's methods and variables are not colored in because they don't exist yet. You must create an instance from the class before you can call the methods and before the variables can have any values. In comparison, an object's methods and variables are filled in with color indicating that the object actually exists and you can use it. You can send the object a message and it will respond by performing the method and perhaps modifying the values of the variables. The Benefit of Classes Objects provide the benefit of modularity and information hiding.
Classes provide the benefit of reusability.
Bicycle manufacturers reuse the same blueprint over and over again to build lots of bicycles. Software programmers use the same class over and over to again create many objects.