Why is it called ''a white city''?

There are many cities and places referred to as 'White City'. One link below for the 1893 World Exposition held in Chicago, IL USA which was nicknamed 'The White City'. The other link is a list of all the places in the world that are called 'white city' with links to each to learn more. Hopefully, the 'white city' that you're looking for is on these links.