I don't know what u mean by primary purpose light colors but if you just asking for primary colors these are the only ones.
Answer:Because they dont want to get hurt
Explanation:
Rukmani feels especially saddened by Old Granny's death because she would have been able to help her.
Old Granny died of starvation and because Rukmani was busy trying to solve her own family's trouble, she was not able to help Old Granny. She even accepted Old Granny's last Rupee as a gift for her grandchild, not thinking that Old Granny needed the Rupee more to buy herself some food.