Hazel eyes appear to shift color depending on the surrounding light or clothing. This variability results from a combination of pigments and optical effects. Hazel typically features a blend of brown, green, and gold tones across the iris, ranging from lighter amber-green to darker brown-gold.
The Unique Optical Mechanism of Hazel Eyes
The unique appearance of hazel eyes results from the interplay of light and two main components within the iris. The brown and gold colors come from melanin, the same pigment that determines skin and hair color, which is concentrated in the anterior border layer of the iris. Hazel eyes contain a moderate amount of melanin, placing them between the high concentration found in brown eyes and the low concentration found in blue eyes.
The perception of green or blue is a result of structural color, dependent on how light scatters through the iris’s stroma. This phenomenon causes shorter wavelengths of light, such as blue and green, to scatter back toward the viewer. Hazel eyes also contain the yellowish pigment lipochrome, which, when combined with the scattered blue light, creates the appearance of green. Because the distribution of melanin is not uniform, different areas of the iris absorb and scatter light differently, leading to the characteristic multi-color effect.
Recognizing the Distinct Visual Patterns
While there are no formal scientific “types” of hazel eyes, the visual patterns created by the pigment distribution are distinctly recognizable. The most straightforward pattern is the standard hazel, where the brown, green, and gold colors blend relatively evenly throughout the iris, creating a subtle, mixed tone. This pattern responds to the amount of light absorbed by the moderate melanin concentration.
A common variation often mistaken for a type of hazel is central heterochromia, defined by two distinct color zones. In this pattern, the area immediately surrounding the pupil is a different color, typically a gold or brown ring, while the outer portion of the iris displays a second color, frequently green or blue. This two-toned ring structure causes the eyes to appear intensely multi-colored, leading to their visual classification as hazel.
The overall shade of hazel is further categorized into light versus dark variations, determined by the density of melanin. Dark hazel eyes contain a higher concentration of melanin, giving them a dominant brown or copper appearance with only flecks of green or gold. Conversely, light hazel eyes have a lower melanin density, allowing the green or amber tones to be more dominant and making the color more responsive to changes in external lighting.
How Hazel Differs from Green and Brown
Hazel eyes are fundamentally defined by their multi-toned nature, which sets them apart from the more uniform colors of brown and green. Brown eyes possess the highest concentration of melanin, which absorbs most incoming light, resulting in a solid, deep color. They lack the multi-toned combination necessary for classification as hazel.
Green eyes typically have a lower, more uniform concentration of melanin than hazel. Their solid green hue results from low melanin, the presence of lipochrome, and the back-scattering of blue light. Hazel eyes, in contrast, must display two or more distinct colors—brown, gold, or green—distributed in a pattern across the iris.
The Role of Genetics in Hazel Eye Shade
The wide spectrum of hazel eye shades is a result of polygenic inheritance, meaning multiple genes influence the final color, not just a simple dominant/recessive pair. The most significant genes involved are OCA2 and HERC2, located on chromosome 15, which regulate the amount of melanin produced and distributed. OCA2 produces the P protein, which is crucial for melanin storage.
HERC2 acts as an upstream regulator, influencing OCA2 expression. Variations in these genes determine the exact amount of melanin present, dictating whether the resulting color is a lighter, greener hazel or a darker, browner hazel. The complex interaction between these and other genes explains why the inheritance of a specific hazel shade is less predictable than the inheritance of a deep brown or blue color.