**Core Concept**
Negative staining is a technique used in microscopy where the background is stained, leaving the cells or microorganisms unstained. This method is particularly useful for viewing certain types of cells or microorganisms that are difficult to stain using traditional positive staining techniques. The **principle of negative staining** relies on the difference in density between the specimen and the background.

**Why the Correct Answer is Right**
Since the question is incomplete, let's discuss the general principle of negative staining. In negative staining, the **background** is stained with a dye, typically a negatively charged molecule that repels the similarly charged molecules on the surface of the cells or microorganisms, thus leaving them colorless. This technique is useful for observing the morphology of cells without fixing or distorting them.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific details of option A, it's challenging to provide a precise explanation. However, in the context of negative staining, any option that suggests the specimen itself is stained would be incorrect.
**Option B:** Similarly, without specifics, if option B implies that negative staining involves staining the specimen directly, it would be incorrect.
**Option C:** If option C suggests a method that does not involve contrasting the specimen with a stained background, it would not accurately describe negative staining.
**Option D:** Without details, if option D proposes a mechanism that doesn't align with the principle of staining the background to contrast with the specimen, it would be incorrect.

**Clinical Pearl / High-Yield Fact**
A key point to remember about negative staining is its application in microbiology, particularly for observing the capsule of certain bacteria, such as *Klebsiella pneumoniae*, which does not take up stain easily. This technique is crucial for identifying such microorganisms based on their capsule's presence and morphology.

**Correct Answer:** Correct Answer: D. The specimen remains colorless.