What is the cause behind the colour change of Taj Mahal from white to yellowish?

The cause behind the colour change of Taj Mahal from white to yellowish is pollution. Air pollution is one of the major contributors as urbanization has left Agra with fewer trees and more carbon dioxide. Lots of harmful gases are emitted from Vehicles like oxides of Nitrogen and Sulphur. When rainwater mixes with these gases they pour down as acid rain. Acid rain is also one of the reasons for the change of colour of the Taj Mahal.