I have suffered with cold hands through countless winters with white/yellow/blue (any color except skin-color) fingers. Raynaud's leaves my fingers and toes constantly cold and without proper circulation. When you combine a stressful environment with the cold winter months it can be a recipe for disaster when it comes to circulation in my fingers. I can't use my mobile phone outside as my fingers with lose all feeling if they are not kept firmly in my pockets.
There are actually a variety of different types of hand warmers on the market today. Check this great article on the different types of hand warmers available and where to purchase them. The reusable gel hand warmers I described above are actually a lot more inexpensive than I had thought. Happy warm hands!