Changing default background color to #0C0C0C causes a different shade of black to appear in areas where there is text or whitespace. Bug or not?

[zch]

I have a color I'd like to set the ``default'' background face to, which
is #0C0C0C. I set the color, but the actual color that gets set is
#0B0B0B. And the #0C0C0C color appears as a separate background color on
all areas of whitespace and text: https://0x0.st/sD9G.png - You may have
to zoom in a considerable amount to see what I'm talking about.

And this issue does not happen with other colors it would seem:
https://0x0.st/sD9k.png - Only with colors that are slightly brighter
than black.

Even with a fresh emacs session, ``emacs -Q'' does not alleviate the
issue https://0x0.st/sDO1.png

There is no face causing this as no other face contains #0C0C0C or
#0B0B0B, I made a search through every single face.

Is this a bug? I'd like to have #0C0C0C as my background color without
this other shade of black appearing as well, it's a bit distracting
though ignorable if I don't think about it.