Entities that glow in the dark or that have emissive layers in their textures aren't affected by the darkness pulsing effect, making visual inconsistencies due to how light sources are affected by it. The resolution of MC-249877 leads me to believe that this isn't intended so i reported it.

Expected result

These entities would get affected by the darkness pulsing effect, being consistent with ambience / fog fade.

Observed result

These entities still glow unaffected by darkness, the pulsing effect only shifts their texture color slightly.

How to reproduce

1. Summon any of the mobs shown in the attachments.
2. Apply yourself the darkness effect.
3. Notice how the pulsing effect doesn't affect them.