I think colorList is the List which store above light,amber,brown,dark values. But it newer decalre any where. Later in page 557 they have given the tag handler class but its not declare there and even we cant declare it there also know since its a java class it gives error when you just declare a list outside a method and add values to it. I think its also not possible to declare it in the Servlet which handle the form submit becuse its too late. So where should it be declared?
You'll find the same tutorial here, from the author of the book. The author says that the attribute is set in the goToForm.do servlet (although it uses sessionScope instead of applicationScope). You can try to put it in the application scope instead.