**Core Concept**
The Munsell scale and lab system are tools used in dentistry to quantify and classify colors. They are based on the principles of color theory, which aim to describe and categorize colors in terms of their hue, saturation, and lightness.

**Why the Correct Answer is Right**
The Munsell scale and lab system are designed to measure the quantity of color, specifically the amount of pigment present in a material. This is done by assigning a numerical value to the color, which represents its level of lightness (value), saturation (chroma), and hue. The system allows for precise measurements and comparisons of colors, making it useful in dentistry for tasks such as shade matching and color selection for dental restorations.

**Why Each Wrong Option is Incorrect**
**Option B:** The quality of color refers to the aesthetic appeal or beauty of a color, which is subjective and cannot be measured by the Munsell scale or lab system.

**Option C:** While the Munsell scale and lab system do provide information about the hue, saturation, and lightness of a color, they do not measure both the quantity and quality of color.

**Option D:** The Munsell scale and lab system are, in fact, used to measure the quantity of color, so this option is incorrect.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the Munsell scale and lab system are based on a three-dimensional color space, which allows for precise measurements and comparisons of colors. This understanding is critical for accurate shade matching and color selection in dentistry.

**✓ Correct Answer: A. Quantity of color**