Sam, Who Has a Retail Clothing Store, Orders 50 White

Sam, who has a retail clothing store, orders 50 white shirts from XYZ manufacturer. He later calls a representative of XYZ and requests that blue shirts be sent instead. The representative agrees. Sam gets white shirts and complains. The XYZ representative says that blue shirts are more expensive because they are in greater demand and that there was no consideration for the modification to the contract. Which of the following is the correct resolution of the dispute?

A) Sam is correct because under the UCC no additional consideration was needed.
B) Sam is correct because a valid unilateral contract existed.
C) The XYZ representative is correct because no additional consideration was provided.
D) The XYZ representative is correct because no valid bilateral contract existed.
E) The XYZ representative is correct both because no additional consideration was provided and because no valid bilateral contract existed.