I was just looking into the cultural experiences that can be had in India and one of the things that was mentioned was the Diwali. According to one site, this is a 5-day festival representing the start of the Hindu New Year.
Also called the "Festival of Lights", you can expect fireworks, small clay lamps, and candles lit during the celebrations to represent victory of good over evil. This festival is said to fall in either October or November each year, depending on the cycle of the moon. This year, it will fall on October 30 and October 19 in 2017.
Holi, or the Festival of Colors, as you mentioned, is also another festival to look forward to; celebrating the abundance of the spring harvest season.
Ganesh Chaturthi is also another cultural experience on can have. Imagine this is an 11-day event honoring the birth of Lord Ganesha, a Hindu elephant-headed god.