The color of human hair and animal fur is determined by the concentration of two pigments: eumelanin and pheomelanin. The node’s associated parameters are Melanin and Pheomelanin.

The concentration of eumelanin is the determining factor of a hair’s color from black and brown to blonde. Black hair has the highest concentration of eumelanin, while blonde hair has the lowest concentration. White hair, on the other hand, completely lacks eumelanin. The second pigment, pheomelanin, gives hair a more orange or red tone.

The shader supports two modes to define fur/hair color.

• Physically Based calculates the color by using the pigment concentrations of Melanin (eumelanin) and Pheomelanin. You can get appropriate values from scientific papers and measurements, e.g. from here.

  

• Artistic uses the Melanin and Redness parameters to calculate the color. Redness adds a red tone to the hair.

  

The Physically Based mode is purely based on Eumelanin and Pheomelanin. This could make it difficult to find working Pheomelanin values if you want shift colors to orange and red. The first image illustrates that you’ll also change the hair’s luminance when you increase Pheomelanin (= vertical direction of the gradient), not only its red component.

The Artistic mode is more intuitive if you want to tune the look manually, because the shift towards a more reddish color doesn’t increase luminance (second image) - at least not as obvious as with the node’s Physically Based option.

The node provides two outputs: color and absorption. You can use the color output to visualise a final color for debug purposes. For both shaders Karma Fur and Karma Hair, which have an absorption input, we recommend using the absorption output. The raw absorption coefficient avoids any color deviations. Deviations occur when you promote the color output to a baseColor input of the Karma Fur and Karma Hair shaders. This leads to multiple bounces between hair strands and creates over-saturation effects.