In AltAz coordinates (=Horizon) *and* color mode the background isn't true black unless one zooms to ~5 ° or narrower.
Any other coordinate mode in color, or choosing Black and white or red night mode have true black background. It is just the combination ** "horizon" coordinates + color mode + views larger than 5 ° ** that is not true black.
This is very noticeable with the OLED screen of my Samsung tablet. This type of screen is ideal for dark adaptation since black is true black, no light leaking. I would like to use the "Horizon" coordinates in color mode, but to preserve the dark adaptation is better that the background is true black at any magnification.