Here my proposal for the "Collider Object": just like the sprite object, with the difference that it stores in the memory only a monochromatic form.
Making colliders with the sprite object it's a waste of memory, since the informations about the aspect of the object are stored as a bmp, while the object will never actually appear in the game.
That's practically unrelevant in case of, i.e., a platform game character, but it could become essential in case of a beat'em up: several big characters, each with its ows colliders -> fighter's memory occupied doubles (and in that case we talk about several MB).
It could also be used for defining areas, as it can do Overlay object in MMF (i.e. where in the point-and-click adventure the character can walk; different terrain reactions on a golf game, and so on...)
Hope I made the point clear enough. It would increase efficiency in Construct (and solve some dramatic cases, like in the Beat'em up example). Why to store useless .bmp graphics when using colliders & similar?