The city is known as the “Sun City” for the bright, sunny weather it enjoys all the year round. It is also referred to as the “Blue City” due to the vivid blue-painted houses around the Mehrangarh Fort, Jodhpur , India
As per wiki pedia : Why blue city : It is thought that Brahmins – members of the priestly class – first took to coloring their houses blue to signify their domicile and to set them apart from the rest of the population. Soon, however, the rest of the population followed suit.
What local people believes : As the city is also know as sun city. Blue is color which will reduce the temperature of their houses as it becomes very hot outside in sunny day . Also blue color last for years thn any other color.