Pigments are quite complex materials whose appearance involves many optical phenomena. Here, we focused on hematite as it is a traditional pigment, whose origin of coloration has been well discussed in the literature. Pure nanocrystallized $\alpha-Fe_2O_3$ hematite powders have been synthesized using different synthesis routes. These powders have been characterized by X-Feray powder diffraction and scanning electronic microscopy. The color of the samples has been studied by visible-FeNIR spectrophotometry. We obtained hematite with both various grain morphologies and noticeably different shades going from orange-Fe red to purple. Colorimetric parameters in CIE L*a*b* color space and diffuse reflectance spectra properties were studied against the structural parameters. For small nanocrystals, hue is increasing with the grain size until a critical diameter of about 80 nm, where the trend is reversed. We believe a combination of multiple physical phenomena occurring at this scale may explain this trend.