Unless we want to be pedantic and take the ambient light reflected off the screen into account. Old CRT monitors, for example, reflected a lot of ambient light

Unless we want to be pedantic and take the ambient light reflected off the screen into account. Old CRT monitors, for example, reflected a lot of ambient light and looked grey when turned off in a lit room. And even when operating in a dark room there would be some diffusion from the lit areas of the screen, which is why they did not actually have "perfect blacks" like many believe. If you had a very dark scene you would have less internal diffusion too though so it would indeed look very good. Something similar could be happening in OLEDs, but yeah IMO OLEDs have perfect blacks for all intents and purposes.