Matthew is right. Make a pen set for Archicad, using the colors you want in Autocad, for instance the old standard pen #1 is red 0.25, etc. Make sure all the pens you use match your Autocad pen settings.
Stick to that pen set in all views and layouts you want to export. (We've saved eons of time after we adopted this pen set as office standard)
Then only use the
Keep Index Number translator. Copy it and make any other tweaks you like, but don't change the default color adjustment button settings. (If you're really into tweaking, you can edit the translation table included, but then you'd have to use a separate one for importing)
If you also import dwgs, please note that how the translator is working at import also depends on which way you open the file. But the KPIN translator is the only one allowing a consistent round-trip.
More info here:
http://archicad-talk.graphisoft.com/viewtopic.php?p=117842#117842
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1