I just got curious about the purple lips and came across this. Also called blue Lips.

The following medical conditions are some of the possible causes of Blue lips. There are likely to be other possible causes, so ask your doctor about your symptoms.

Cold weather
Low body temperature
Cyanosis
Inadequate oxygen circulation
Smoking
Anemia
Iron deficiency anemia
Certain circulatory disorders
Certain heart disorders (see Heart symptoms)
Congenital heart disorders
Certain lung disorders
Asthma
Bronchitis
Chronic bronchitis
Pneumonia
Emphysema
Pulmonary thrombosis
Pulmonary embolism
Pulmonary edema
Airway foreign body
Fibrosing alveolitis
Pneumoconiosis
Extrinsic allergic alveolitis
Coughing
Croup
Fume inhalation
Laryngeal edema
Shock
See also blueness and cyanosis