The use of a darker foundation on the neck compared to the face will make the neck appear:

Using a darker foundation on the neck compared to the face can create a visual effect that makes the neck appear thinner. This is because darker shades can create a shadowing effect, which can help contour and define the shape of the neck. When the neck is darker, it can recede visually, thus drawing attention away from it and creating a more elongated and slender appearance. This technique is often employed in makeup to enhance facial features and create balance between different areas of the body.

In contrast, a lack of contrast between the face and neck can make both areas appear more uniform, which may not always be flattering. The interplay of light and shadow is crucial in makeup artistry, as it can dramatically influence how features are perceived. The application of a darker shade in this context aims to achieve a more refined look, allowing for better definition and a more polished overall appearance.