Frame around the window.

[Gisele]

I need to know what's this pink border frame, so I adjust its color/material.

When I isolate the window, I do not see it. Attached are screenshots showing the window's settings.

[Mahmoud Qenawi]

This is window casing, you can check it's parameters via this dialog.

https://help.graphisoft.com/AC/26/INT/index.htm?rhcsh=1&rhnewwnd=0&rhmapid=#t=_AC26_Help%2F150-1_Doo...