user: Describe Inputs from the Blender manual or Python API, including usage steps and snippets.

assistant: ### Common

Color
:   The RGB color of the strand. Only used in Direct coloring.

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    Coloring hair using the Direct coloring parametrization. (The numbers on top are the RGB values.)

Melanin
:   Absolute quantity of pigment.
    Range \([0, 1]\) equivalent to \([0\%, 100\%]\).

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    Melanin.

Melanin Redness
:   Ratio of pheomelanin to eumelanin.
    Range \([0, 1]\) equivalent to \([0\%, 100\%]\).

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    Melanin Redness.

Tint
:   Color used for dyeing the hair after applying the melanin pigment.
    It is not subject to randomization.
    It can be disabled by setting the color to white.

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    Tint, using Melanin 0.1 and the corresponding RGB values.

Absorption Coefficient
:   Attenuation coefficient \(\sigma\).

IOR
:   Index of refraction ([IOR](../../../glossary/index.html#term-IOR)) defining how much the ray changes direction.
    At 1.0 rays pass straight through like in a transparent material;
    higher values give more refraction.
    Default value is \(1.55\).

Offset
:   Tilts the glint of the hair by increasing the angle of the scales of
    the hair’s cuticle with respect to the hair shaft.
    Human hair usually has low values.

Random Color
:   For each strand, vary the melanin concentration by \(RandomFactor\).
    Range \([0, 1]\) equivalent to \([0\%, 100\%]\) of
    the initial melanin concentration.

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    Random Color.

Random Roughness
:   For each strand, vary both Roughness values by \(RandomFactor\).
    Range \([0, 1]\) equivalent to \([0\%, 100\%]\) of
    the initial roughness values.

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    Random Roughness.

Random
:   Random number source. If no node is connected here, it is automatically
    instanced with the value obtained from Hair Info ‣ Random.

### Chiang Model

The Chiang model is based on a Gaussian distribution with separate roughness
along and orthogonal to the hair.

Roughness
:   Specify how much the glints are smoothed in the direction of the hair shaft.
    Too low values will smoothen the hair to the point of looking almost metallic,
    making glints look like [Fireflies](../../../glossary/index.html#term-Fireflies); while setting it too high will result in a Lambertian look.

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    Roughness.

Radial Roughness
:   Specify how much the glints are smoothed in the direction of the hair normal.
    Too low values will concentrate the glint;
    while setting it too high will spread the light across the width of the strand.

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Radial Roughness.

Coat
:   Simulate a shiny coat of fur, by reducing the Roughness to the given factor
    only for the first light bounce (diffuse).
    Range \([0, 1]\) equivalent to a reduction of \([0\%, 100\%]\) of the original Roughness.

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    Coat.

### Huang Model

The Huang model is based on microfacet based reflection and transmission,
and supports elliptically shaped hair.

Aspect Ratio
:   The ratio of the minor axis to the major axis of an elliptical cross-section.
    Recommended values are 0.8~1 for Asian hair, 0.65~0.9 for Caucasian hair, 0.5~0.65 for
    African hair. The major axis is aligned with the curve normal, which can be created
    with geometry nodes, but is not supported in legacy particle hair.

Roughness
:   Microfacet roughness for reflection and transmission.

Reflection
:   Optional factor for modulating the first light bounce off the hair surface.
    The color of this component is always white. Keep this 1.0 for physical correctness.

Transmission
:   Optional factor for modulating the transmission component. Picks up the color of the
    pigment inside the hair. Keep this 1.0 for physical correctness.

Secondary Reflection
:   Optional factor for modulating the component which is transmitted into the hair,
    reflected off the backside of the hair and then transmitted out of the hair. This
    component is oriented approximately around the incoming direction, and picks up the
    color of the pigment inside the hair. Keep this 1.0 for physical correctness