What distinguished Jamini Roy as a modern Indian artist?

His rejection of academic training

Answer:  His rejection of academic training
Jamini Roy, after undergoing academic training in the colonial Art School, rejected it in favor of adopting the flat and colorful style of folk painting.

Jamini Roy is a unique example of modern Indian artist, who after undergoing academic training in the colonial Art School rejected it only to adopt the flat and colourful style of folk painting seen in villages. He wanted his paintings to be simple and easy to duplicate to reach a wider public and based on themes like women and children, specifically, and rural life, generally. However, the struggle between the Indian and European taste in art continued as seen in the art policy of the British Raj. For example, the project for mural decorations for Lutyen’s Delhi buildings went to the students of Bombay School of Art, trained in realistic studies by its Principal, Gladstone Solomon. On the other hand, the Bengal School artists were allowed to decorate the Indian House in London under close British supervision.