In 2011, somebody dared to asked the same question:
And was told to RTFM with a general link to the startpage of the documentation (...).
It's not just about colors, they're diferently shaped icons too. What do they mean, so I can try to understand what the program thinks the problem is after a lookup without having to post question after question on this forum.
Even a search in our WWW-search engine gets no hits in page1.