"LOL PJF, yes - it almost makes sense."

Frack me, that's more than I could've hoped for.

It's all a contrast effect, as with most of what our eye/brain mechanism sees.

If you look at the sun through a suitable filter, you'll see dark sunspots against the white background of the overall solar disk. This despite the fact that the light from the sunspots and the disk is all bright enough to blind you in an instant without the filter. That's contrast.

Likewise with seeing nebulosity in the night sky (naked eye or with telescope). The 'stuff' that bounces and bends (and absorbs and re-emits) light to make nebulae is less dense by a hundred times the best vacuum that mankind can manage on Earth. It's the contrast of this dim, dim light against the pure black of space that makes it visible.