Forum OpenACS Q&A: Response to Different image and css path with SSL?
I think I fixed this problem partially (it was a bug) and the discussion is here.
I generated a patch and Don said he would apply it, but I'm assuming he will apply it to the 4.6/development branch, not the 4.5 final branch. So if you need a copy it is in SDM here.
Probably, however, the best "fix" for your problem is to add URLs to ad_login_page in packages/acs-tcl/tcl/security-procs.tcl so files from your graphics and css directories will get served via https without redirecting to a login.