Based on the exhibits provided, the developer has set up an Invoke Method activity to add an item to the "Colors" list variable. The list is initially declared with two items "Red" and "Green". The Invoke Method activity is configured to add the string "Yellow" to this list.

The properties of the Invoke Method activity indicate that the method 'Add' will be called on the target object 'Colors' with the parameter "Yellow". This means the string "Yellow" will be added to the end of the list.

The outcome of executing this Invoke Method activity will be:

D. Colors will contain items in the following order: "Red", "Green", "Yellow".

This is because items in a List in .NET are added in sequence, and the "Add" method appends the new item to the end of the list.