Diwali - India's festival of lights,
This colourful pattern is called rangoli.
Diwali to my mind is basically a giant nationwide form of house cleaning for a very esteemed VIP guest, a certain goddess of wealth. This huge operation spearheaded by the women of each household involves cleaning all aspects of the house and goes on to decorating all aspects of it and on the big day lighting it up with as many diyas [small earthen lamps] as humanly possible
Read more about it here.