The optical properties of hair fibers were studied, focusing on the reflections (highlights) from both the front and the back surfaces of the fiber in consideration and on the effect these have on the perceptions of hair appearance. The two reflections are distinguished from each other by sight, because only the back surface reflection is colored by melanin granules and/or dyestuffs inside the fiber. When we observe a flat plate as a model for hair without a cuticle structure, the visual angle between the two light loci correlates with the thickness of the model plate and gives an impression of depth. In the case of hair with a cuticle angle, the visual angle is maintained even when the fiber thickness is reduced. This visual angle causes an overestimation of the thickness and enhances the impression of depth. The visual angle changes dramatically with a curl curvature change of the hair tress, meaning that the impression of depth is also dynamically changed by a small change in hairstyle. The dynamic change in the impression of depth probably causes a vibrant impression. The following are required for beautiful hair appearance along with an impression of depth and vibrancy: (a). Internal structure without light scattering origins is essential to observe vivid colored highlights from the back surface. (b). Well-ordered cuticles are essential to get intensive double highlights from the front and back surfaces. (c). A properly curved hairstyle is essential to obtaining a more vibrant impression.