The reason why you are seeing this message is that ContinuousTests takes a lot more than test coverage into account when giving feedback. With the margins that you see there you can get either green, yellow or red. Green means that changing this code is fairly safe. Yellow means that there is a bit of a risk changing that piece of code. Red means that if you change this code you are on your own. There is a good chance something will break if it is changed. If you hover over the icon you can see some statistics about the risk. If you right-click and choose "ContinuousTests->Get Affected Graph" you will see the coupling graph for this piece of code.
When the "here be dragons" message is shown it means that the code you are looking at is referenced at a lot of places in the code and no tests seems to be coupled to it or what is referencing it. So changing that code you are risking not only breaking that method but also breaking everything that indirectly uses it.
Hope that explains it.