Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Color
HAIR_SHADER_COLORParameter: Diffuse
HAIR_SHADER_DIFFUSE_STRENGTHParameter: Texture
HAIR_SHADER_DIFFUSE_SHADERParameter: Specular
HAIR_SHADER_SPECULAR_STRENGTHParameter: Sharpness
HAIR_SHADER_SPECULAR_POWERParameter: Texture
HAIR_SHADER_SPECULAR_SHADERParameter: Strength
HAIR_SHADER_ISPECULAR_STRENGTHParameter: Sharpness
HAIR_SHADER_ISPECULAR_POWERParameter: Texture
HAIR_SHADER_ISPECULAR_SHADERParameter: Roughness
HAIR_SHADER_ROUGHNESSParameter: Variation
HAIR_SHADER_ROUGHNESS_VARParameter: Reflectiveness
HAIR_SHADER_REFLECTParameter: Translucence
HAIR_SHADER_TRANSMITParameter: Shadow
HAIR_SHADER_SHADOWParameter: Alpha Depth
HAIR_SHADER_ALPHA_DEPTHParameter: Shadow Transparency
HAIR_SHADER_SHADOW_TRANSPARENCYParameter: From Hair Materials
HAIR_SHADER_FROM_MATERIAL