This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Color of hand change to following color, when a patient of Raynaud's disease puts his hand in cold water: 
Select and explain. 
A. White, B. Yellow, C. Blue, D. Black.
A: White
Answer: A: White 
Explanation: None