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.
In hyperpigmentation, the skin either produces too much pigment or the pigment is deposited deep within the skin, resulting in dark spots. When color is lost, it's called hypopigmentation, which results in light-colored patches. All people with dark skin are at risk for both skin conditions. Among the most common types of pigment problems in dark skin is post-inflammatory hyperpigmentation. This occurs as a result of skin injury, such as a cut, scrape, or burn. It can also occur in conjunction with eczema or acne.