The lips and fingernails turn to blue from gray color in

Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs. 

As a result of the infection, the alveoli get filled with fluid leading to severe problems in respiration. 

The symptoms of pneumonia include fever, chills, cough and headache. 

In severe cases, the lips and finger nails may turn gray to bluish in colour.