White is the color of transparency & dignity. Since Indian independence movement, there was a custom by Indian freedom fighters like Gandhi and other political leaders to boycott foreign clothes and adopt Khadi clothes. Khadi is particular means to hand knitted homespun white clothe. Later it became a trend for political leaders to wear white Khadi and Gandhi cap. The white cap (Gandhi cap) first emerged by Gandhi during 1918 to 1921; later it became a standard dress code of all Congress people. Gandhi cap with khadi is still a custom in rural areas of Maharashtra. So, white dress with cap is just a custom for Congress leader's that was adopted by other political parties in India with different colors and styles. BJP people used to wear saffron clothes and communist party uses orange with green colors, etc.
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