## Core Concept
Addisonian pigmentation refers to the characteristic skin and mucous membrane changes seen in patients with Addison's disease, which is primary adrenal insufficiency. This condition results from the deficiency of cortisol and aldosterone due to adrenal gland destruction. The pigmentation changes are primarily due to the elevated levels of adrenocorticotropic hormone (ACTH) and other pro-opiomelanocortin (POMC) peptides.

## Why the Correct Answer is Right
The correct answer is related to the understanding that Addisonian pigmentation is primarily caused by the increased levels of ACTH, which stimulates melanocortin 1 receptors on melanocytes, leading to an increase in melanin production. This results in characteristic pigmentation changes, including darkening of the skin, especially in areas exposed to the sun, and mucous membranes. The pigmentation can also occur in scars and recent wounds.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, Addisonian pigmentation involves an increase in skin pigmentation that can be generalized but often is more pronounced in sun-exposed areas, recent scars, and mucous membranes. If option A denies these characteristics or suggests an atypical presentation not associated with Addison's disease, it would be incorrect based on the specifics of the statement not provided.
- **Option B:** If option B accurately describes a feature of Addisonian pigmentation, such as its occurrence in sun-exposed areas or mucous membranes, then it would not be the correct answer because it aligns with known facts about the condition.
- **Option C:** Similar to option A, if option C describes a known aspect of Addisonian pigmentation, it would not be the correct answer. Without specifics, we assume it could relate to the pathophysiology or clinical presentation.
- **Option D:** This being the correct answer implies it does not fit with the established facts about Addisonian pigmentation.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Addisonian pigmentation often precedes other symptoms of Addison's disease and can be a crucial diagnostic clue. The pigmentation changes are due to the elevated ACTH levels, which can also cause hyperpigmentation in other conditions, such as ectopic ACTH-producing tumors.

## Correct Answer: D.