Answer: The fur color of the arctic fox will be brown.
Explanation: If the pollution caused the snow to become brown. The Arctic fox will change its fur color to brown and this will easily hide the fox from predators that is present in the snow.
The fox will need to have a darker fur in winters. In today's urban areas the pollution will hide the things in darker shade.
The foxes' fur would also turn dark. In order to adapt with the surrounding environment. This is evolution, but would happen slowly over many generations