Mask border color question

If I add say a rectangle mask node, the border of the mask is green. If I click on the border and drag it and re-size it it turns red. If I deselect the mask node and re-select it it reverts back to green.

Is the red an indicator that the boarder is currently selected? If so, what affects the border when it is selected? I can not see what keyboard shortcuts that would affect it while it is selected so I am confused as to why it does this red selection indication, if indeed that is what it means.

Thanks!