## Core Concept
Cafe au lait spots are a type of skin discoloration that appears as light brown to dark brown flat spots. They are a common finding in various medical conditions, including neurofibromatosis type 1 (NF1), and can be a key diagnostic feature. The spots are typically oval in shape and can vary in size.

## Why the Correct Answer is Right
The correct answer, , is associated with the characteristic features of cafe au lait spots. Typically, cafe au lait spots are more than 5 mm in diameter in prepubertal individuals and more than 15 mm in postpubertal individuals. They are usually uniform in color and have a clear border.

## Why Each Wrong Option is Incorrect
* **Option A:** Typically, cafe au lait spots are uniform in color, which matches this description, making it an incorrect choice for "all except."
* **Option B:** Oval or rounded shape is a characteristic feature of cafe au lait spots, making this option incorrect for "all except."
* **Option D:** A clear border is a defining feature of cafe au lait spots, which makes this description incorrect for "all except."

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the presence of six or more cafe au lait spots (each >5 mm in prepubertal individuals and >15 mm in postpubertal individuals) is a diagnostic criterion for neurofibromatosis type 1 (NF1). This condition is associated with multiple cafe au lait spots, neurofibromas, freckling in the axillary or inguinal regions, optic gliomas, and Lisch nodules.

## Correct Answer: D. Irregular borders.