The bug
While an ender dragon is in the world, blocks render darker from far away. I'm unsure whether this is intentional or not. The fog in the end that's only present when the ender dragon fight is underway, it too dense making blocks in the distant dark.
Linked issues
discovered while testing
is duplicated by
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Yes, @unknown. Confirmed in 1.16-pre3.
Confirmed in 1.16-pre5.
Can confirm in 20w51a.
Can confirm in 21w03a.
Can confirm in 21w05a.
Can confirm in 21w06a.
Can confirm in 21w07a.

I thought that was intended. As when you kill the dragon, you free the end (from the darkness). So this was not the case before 1.15?
Can confirm in 1.16.5 and 21w08b.
Can confirm in 1.17.

Can confirm in 1.17.1 Release Candidate 1.
Can confirm in 1.19.2.

I think the fog during the Ender Dragon fight in The End reduces visibility too much. It makes it difficult to see if the End Crystals on the taller Obsidian Pillars have been destroyed, and sometimes it's also hard to see where the Ender Dragon is.
Can this still be reproduced in 1.16-pre3?