The story
Transliteration of Hindi भगवा (bhagvā, “saffron”). Saffron is a sacred colour in Hinduism. According to Hindu belief, it is the color of Sandhya (twilight) and Agni (Fire) which symbolises sacrifice, light, and quest of salvation. It was used in flag of Maratha Empire. Later in 1925, a variant of this flag was adopted by ultra-nationalist Hindtuva group Rashtriya Swayamsevak Sangh thus beginning its association with Hindu nationalism.
Etymology from Wiktionary, CC BY-SA 4.0.