I spent a few days in the blue city of Jodhpur, Rajasthan on my way through to New Delhi and the Himalayan north. The paint used on so many of the buildings contains copper sulphate which is an effective insect repellent. It also commonly turns blue.
A great thing to do in Jodhpur is to visit the Merangarh Fort high up on a hilltop in the middle of the city. From the fort there are any number of wonderful lookouts that give you the chance to see the city spread with its beautiful shades of blue, in the middle of a semi-arid desert. One of the best places I've ever visited and one of 5 blue cities on this planet apparently.