Different colors mean different things.
Black is an oil system hit. You have a limited amount of time before your oil runs out and your engine just plain stops.
Grey is a radiator system hit. This is only on planes that have them. The A6m does not. Once your radiator is dry (very fast) your engine overheats in seconds and dies.
White is a fuel system hit. In planes with only 1 main tank this is rather serious (F4us, 109s, etc). In planes that break the fuel into 1 or more tanks, each individual tank can have a fuel leak. Those tanks will drain quickly, but the other tanks (the ones still intact) will not drain. YOu need to switch your fuel selection to the leaking tank, to use up as much of the draining gas as possible, and then when it's gone switch back to your other tanks.
CTRL+D also shows you the damage screen listing. Items in RED are damaged/destroyed.
