OptionaldiffuseLinear transmitted-light RGB in [0, 1] per channel; defaults to [1, 1, 1].
OptionaldiffusesRGB RGB texture multiplied by diffuseTransmissionColorFactor; alpha is unused.
OptionaldiffuseFraction of dielectric diffuse light transmitted through the surface, in [0, 1]; defaults to 0.
OptionaldiffuseLinear alpha-channel texture multiplied by diffuseTransmissionFactor; RGB is unused.
Khronos release-candidate thin diffuse transmission extension, KHR_materials_diffuse_transmission.