If planet 9 exists, is it correct to say that it is a "dark planet"?

By "dark" here I mean to a planet that doesn't reflect enough light to easily be seen from normal telescopes (in the current common telescope technologies of 2021 which I am not familiar with) ; it would just appear in any such telescope so dark to be "swollen" in the dark void, so it just might be very hard to watch it with such a telescope

I would assume that it is indeed a "dark planet" by that definition because I don't think that what makes us humans having hard time to directly watch it short-scale telescopes is all the objects that screening it, rather, the vast proximity of it from the sun which should make it so dark so to be a too dark spot in a dark background and thus a "dark planet" in the similar way to how sunless galaxies would be considered "dark galaxies".