I think it is more a Sketchup thing then a Enscape thing perhaps, but hopefully someone know the answer.
I have had this issue with previous projects, at some point everything which I import or draw automatically becomes a material color. Even if I have selected for example WHITE, it turns in this case to a black color. Also when importing an asset, inside SU it has this black color instead of the default 'white default' color.
Does anyone know what happened?