The N^2 diagram is color and shape coded.
Are the explanations of these included in the manual somewhere?
Some of them can be deduced more easily for example I assume orange one is implicit comp output. But there are combinations of black, gray circle square and surrounded square
To get some information, you can click on the 'Show legend' button (the sixth button starting from the right as for OpenMDAO 2.2.1). The legend is displayed at the bottom.