White material changes with HDRI background

Hello everyone,
I have a really strange problem. I have imported my SketchUp model into Twinmotion via the direct link and customised everything as I would like it to be. However, all the surfaces that were coloured M00 (=white) in SketchUp were not white, but rather beige. Then I changed the HDRI background (to a green landscape) and then the material also turned green (see screenshot). However, when I go to the material properties, the white material is still displayed as white. If I replace the material with a material from the Twinmotion library, it remains green.
I have also tried to hide the ceiling and insert a white surface as a primitive in Twinmotion. However, this is also displayed in green.
Has anyone ever had this problem? I would be very grateful for quick help. Kind regards and thanks in advance, Vanessa

p.s. I realized that it isn’t because of the texture but all surfaces facing down are concerned.