See the question just above yours titled "Late Milestones" which is
essentially the same solution. You just need to use "Finish" in your test.
Play around with something like this ---
Use a formula in a flag field such as Flag1
IIf([% Complete]<>100 And ProjDateDiff([BaselineFinish],[Finish])<1,Yes,No)
You can then format the line based on the state of the flag.
Mike Glenn put up a tutorial on how to format the bars under given
conditions. Please see his tutorial #14 and #15 on this link
http://pubs.logicalexpressions.com/Pub0009/LPMFrame.asp?CMD=ArticleSearch&AUTH=23