I began having the same problem in 1999 inconveniently as we were approaching a house one night to serve a search warrant. Two fingers were blue/"dead"white. The blood comes back at its own pace. I can sometimes speed it up with hot water running over it. I was diagnosed with Raynaud's Disease by a rheumatologist. Unfortunately there is no cure. Fortunately I live in So. Cal. If I touch a cold steering wheel or cold can of soda it happens. I just make sure I always have gloves and stay warm, which isn't always easy. They did give me some nitroglycerine cream to put on the area when it happens but it's not really convenient for the type of work I do. "Excuse me, I can't shoot you right now I have to wrap nitro cream around my finger so it's not blue anymore"
Hope you get some answers.