MonoBehaviour does not have the same colour as your classname. There might be a problem with Visual Studio. Please watch lecture “Fixing Visual Studio Problems” (currently #4).
Have you already compared your code to the Lecture Project Changes which can be found in the Resources of this lecture?
NullReferenceException means that a reference (“link”) to an instance is missing. Double click on the error message to see to which line in your code it is referring. If you exposed a field in the Inspector, make sure that it’s not empty.