The Darkness pulsing effect (i.e. the screen overlay that fades in when the Darkness effect is applied, pulses throughout its duration, and finally fades out when it wears off) isn't entirely smooth in its transitions. This is in contrast to the Darkness fog itself, which fades in and out with buttery smoothness (although the transition to and from the ambient fog is abrupt due to MC-248194). As with MC-269272, this issue is hard to notice in normal gameplay but can be seen at lower tick rates; however, even then this issue is decidedly less noticeable than the former, so a Low priority or even a Won't Fix resolution seems appropriate.

In the attached video, observe the grass and how it changes color haltingly when compared with the fog fadeout at the end.

This issue relates to MC-269272 and MC-249388.