Add an ext_config.ini on the skin folder with this ;)
[INCLUDE: common/materials_carpaint.ini]
CarPaintMaterial = EXT_Car_Paint
DisableDev = 1
[Material_CarPaint_Metallic]
Skins = Senna
BrightnessAdjustment = 0.25
FlakesK = 0.2
ClearCoatThickness = 0.200
ClearCoatTint = 10, 10, 10
BaseSpecularColor = 140,140,130
SpecularBase = 0.8, 10
AmbientSpecular = 2.9
AmbientSpecularEXP = 2.8
[SHADER_REPLACEMENT_...]
MATERIALS = EXT_Car_Paint
PROP_...=ksAmbient, 0.25
PROP_...=ksDiffuse, 0.08
PROP_...= fresnelMaxLevel, 0.25
Hope you will like it ;)