My finger knuckles all look grey as if they're dyed by fabric but I don't think it is. It has come and gone for a couple weeks now.

Gray skin. This is hard to answer without a lot of other information. If its just the knuckles it would suggest you are getting something on your skin externally. IF this is an internal problem I would think of hemochromatosis (too much iron in the body) or some chronic kidney problem. Some dietary extremes can also cause gray skin issues. Generalized lack of oxygen to a body segment would also be a thought,