Which observation might indicate cyanosis?

The observation indicating cyanosis is the blueness of lips. Cyanosis is characterized by a bluish discoloration of the skin and mucous membranes, which typically occurs due to insufficient oxygen in the blood. The lips, being highly vascular and exposed, often show this bluish tint as a visible sign of hypoxia or inadequate oxygenation.

When evaluating the remaining options, redness of the lips does not indicate cyanosis; instead, it may suggest increased blood flow or irritation. Swelling of the hands is also unrelated to cyanosis, as it may indicate inflammation or fluid retention rather than oxygenation issues. Blurred vision, while it could suggest other medical conditions, is not a symptom that assesses oxygen levels and therefore does not relate to cyanosis. Thus, the correct observation associated with cyanosis is indeed the blueness of the lips.