What do the colors mean?

So I get what green means in the progress bar, but what about yellow and red/pink?  Pink is apparently an error of some sort, but how is that different from yellow?  I seem to get yellow sometimes with no errors listed at the end.  I cannot find any color key anywhere in the program.  It's not under Preferences or Options.  Here on the help pages, its not in the FAQs or the manual.