Question

2) What did the narrator do which changed the colour of Nicola's face?

Answer 1

Seeing them always working so hard at various jobs, the narrator one day dared to ask them why they spent so miserly on their personal needs such, as food, clothing, etc, in spite of earning quite some money. He inquired of them what they did with their money. These questions changed the colour of Nicola's face.  

Answer 2

Nicola and his friends never spended so much money that has small requirements always.when narrated askked the boys about the money they spent Nicola felt scared and turned pale.this embarrassment and fear changes the colour of his face