You never know when set notation is going to pop up. Usually, you'll see it when you learn about solving inequalities, because for some reason saying x < 3 isn't good enough, so instead they'll want you to phrase the answer as the solution set is { x | x is a real number and x < 3 }.
If the skin really looks like the color of ash, a deeper more persistent gray or gray-blue color, this could potentially be due to a side effect of certain medications, with or without interaction from sunlight.
Cyanosis is a bluish hue to the skin, gums, fingernails, or mucous membranes caused by a lack of oxygen in the blood.When blood is fully oxygenated it appears bright red; when it lacks oxygen supply, the blood is a dark purple or bluish red.This lack of oxygen in the blood supply to a body part, such as the nail bed, skin, or mucous membrane, causes that body part to take on a bluish tint.Oxygen is present in your blood through hemoglobin, a red blood cell protein that carries oxygen.his lack of oxygen in the blood supply to a body part, such as the nail bed, skin, or mucous membrane, causes that body part to take on a bluish tint.