[jacquesm]

That's not what 'Dark' means in this context. It's not that it is too far away to be detected, it is non-luminous (as in: not emitting any electromagnetic radiation) and so it isn't detectable other than by its secondary effects on other objects.

Black holes are another example of something that we can not directly observe using instruments, but that we can observe through their secondary effects. But black holes are part of the cosmic accounting book in an identified manner, dark matter is not.