Fig. 2.

Quantitative assessment of eye pigmentation in the CANDELA sample. a Three-dimensional distribution of quantitatively assessed iris colors in the bicone HCL (hue, chroma, lightness) color space. Each dot corresponds to a CANDELA individual and its color represents the average iris color for that person. The color space has a polar coordinate system, where the vertical axis represents L (lightness/brightness, from dark = 0 to light = 1), the horizontal distance from the central axis represents C (chroma/saturation, from desaturated = 0 to fully saturated = 1), and H (hue/ tone) represents the angle when a vertical plane is rotated along the central axis (the three primary colors red (R), green (G) and blue (B) being situated at angles of 0°, 120° and 240° respectively). b The full range of the HCL color space, showing how the three color components vary in the space. Hue varies as a color circle, coming back to red at 360°. The unlabeled axes represent the Cartesian equivalents for the C and H variables, which define a polar coordinate system, as shown in panel a. c Side view of the bicone in a showing how the L (lightness/brightness) and C (chroma/saturation) of eye colors vary among CANDELA volunteers. The position of the dots corresponding to the average eye colors of the sample images in Fig. 1c are indicated. d Top view of the bicone in a showing how H varies among the eye colors of CANDELA volunteers. The position of the dots corresponding to the average color of the sample images in Fig. 1c are highlighted by white circles. In addition to the primary RGB colors, the secondary colors orange (O), yellow (Y), cyan (C) and magenta (M) are shown at their corresponding H angles