That's true but it's also true of some other dark body of the same mass. "do nothing to refracted light" was poor wording, my bad - it's more like gravitational

That's true but it's also true of some other dark body of the same mass. "do nothing to refracted light" was poor wording, my bad - it's more like gravitational lensing is the only thing that happens to its light, as opposed to adding new peaks to the spectrograph and such.