Hi Peter,
Sorry for the missing information. I'm working with Archicad 13 (french version) using the basic objets library 13.
Yes, these lines are the opening lines of the window. I didn't have this trouble with Archicad 10, the previous version I was using.
Following your instructions, it appears that I do not have such an option into the 3d objets settings (see attached file).
I have already tried to change all parameters of the objet itself but the red lines are "resisting"...
I have tried also other kinds of window objets. Same problem in 3d view.
Regarding your last question, the 3d is gray by purpose (gray paint & texture) at this stage of the project.
Thank you Peter.