Final answer:
The nurse should inform the primary care provider that the vascular supply may be compromised.
Step-by-step explanation:
The nurse's most appropriate response in this situation would be to inform the primary care provider that the vascular supply may be compromised. A dark purplish color of the stoma could indicate poor blood flow, which can be a sign of compromised vascular supply. This warrants immediate attention from the primary care provider to assess and address the situation.