Final answer:
Color creates an illusion that helps to guide lines of attention in a hair style by altering perceived density and emphasizing curves.
Step-by-step explanation:
The element that acts as an illusion and helps to create lines of attention in a hairstyle is color. Color can be used strategically to create an impression of different shapes and textures within a hairstyle, effectively guiding the viewer's eye and emphasizing certain aspects of the style. For instance, highlighting and shading can make areas of hair appear more or less voluminous, thereby affecting the perceived density and space. Moreover, color contrasts can accentuate the curves of a hairstyle, creating a visual flow that attracts attention to particular features.