As I understand black holes, they're considered "black" because the escape velocity is, or exceeds, the speed of light. Alternatively, the escaping light is redshifted infinitely.
The Schwarzschild radius of an object is the radius of a sphere with equivalent mass for which the escape velocity is c.
Logically, this effect would occur on a continuum and wouldn't simply be state-dependent. That is, if you add a differential amount of mass to an object repeatedly it will (eventually) gradually redshift out of visibility and become a black hole. It won't simply vanish when the appropriate mass has been collected.
This suggests to me that, somewhere, there exist objects with enough mass to be highly redshifted but not enough to be "black."
Would it be possible to identify such an object from associated effects, such as gravitational lensing, or, without closer inspection, could it simply be mistaken for an extremely hot brown dwarf? (Or option C, is there a reason this couldn't happen?)