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: Dental
All of the following are true about vitiligo except: 
Select and explain. 
A. Autoimmune destruction of melanocytes, B. Vitiligo vulgaris is the most common type, C. Black hair is a poor prognostic sign, D. Koebner's phenomenon positive
C: Black hair is a poor prognostic sign
Answer: C: Black hair is a poor prognostic sign 
Explanation: Since black hair follicle has melanocyte precursors, it is a good prognostic sign.