Twitch,

The gray smoke you see when you start the engine is unburned fuel. When the starter cranks the engine and it doesn't fire, vaporised unburned fuel and air is pushed into exhaust system by the exhaust storke. This grey smoke is then pushed out of the exhaust system by the exhaust gasses when the engine starts to run.

Any non-altitude compensated Diesel engine will smoke black in higher altitudes because the same amount of fuel is injected but less air is pushed into the engine by the lower atmospheric pressure. Thus the mixture is richer and there is not enough air to burn all the fuel.

P E H