When you save a AutoCAD dwg from your ArchiCAD plan you can choose whether the pen colours should use just the ArchiCAD pen numbers or if it should save using the closest matching AutoCAD pen number.
When you save a dwg in the dialogue box that appears there is an
Expert button, when you click this you will see more options one of which is
Match AutoCAD colour table
I prefer to not match AutoCAD colour table as it throws the pen numbers all over the place if the consultant sends the dwg back to you. Also if I was on the receiving end I wouldn't be happy having to set up a new PC2 file to sort out the colours and weights of the pens.
Much simplier to deselect
Match AutoCAD colour table and then Pen 1 in ArchiCAD is Pen 1 in AutoCAD. So then it doesn't matter what colour you use in ArchiCAD
Below is a link to some tips I did for a mate new to ArchiCAD
http://homepage.mac.com/fuzzytnth3/fuzzyblogs/tips/C1514112824/E1672874440/index.html
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics