These jeans, by Naked and Famous, start off blue, and then transform to white with heat. How is this achieved? Well simply by including a “a thermo chromic dyestuff that has a molecule inside, which changes color based on its temperature range." So if you have a cold day outside, you'll have blue jeans. If you have a hot summer day, you'll have white jeans!
You'll have to suffer a bit though as retailers such as Barneys are selling them for $240 a pair.