Not to totally nip a potentially interesting thread in the bud but - sure, people "pale slightly" all the time. I mean, I've certainly seen it. When someone is possibly going to faint, some of them pale a bit (generally, blood moving from their head to their extremities) while others will go white (not to even mention variations in skin tone). It doesn't seem that odd to me at all (plus, there's an alternate reading that you haven't considered - someone blanching - or going "ghost white" as you called it - and then immediately recovering, so that the "slightly" of "paling" is referring to time, not intensity of color).
But, really, seen it quite frequently. Tell someone their mother is dead and they will blanch. Tell someone their dog is dead and they might pale slightly. Obviously, there are a wide variety of human beings with a wide variety of physical/health states experiencing a wide variety of stimulus in the world - why would it be unlilely that such things could happen, even if they haven't been experienced by you?