The bug

When under the Wither and Absorption effects simultaneously, both normal and absorption hearts will turn black to indicate the Wither effect's presence. The issue here is that not only do both heart types look identical under these conditions, but they point to the exact same texture file in the game (rather than different visually identical textures), barring resource pack creators from retexturing them individually.

It used to be possible to texture both of them individually, but this functionality went unused by the game and eventually broke in 20w49a for both withered and poisoned absorption hearts (see MC-207252). Withered absorption hearts were eventually "fixed" in the first 1.17 pre-release (MC-224159), but poisoned and frozen absorption hearts still use the exact same file as normal absorption hearts and are tracked at MC-226845 and MC-226846 respectively.

How to reproduce

A resource pack is attached to this issue that changes the full withered non-hardcore heart texture to the red stained glass texture, and nothing else.

1. Download and apply the attached resource pack
2. Eat an enchanted golden apple
3. Walk into a wither rose

Expected results

Only the normal health bar would turn into red stained glass panes.

Actual results

Both the normal health bar and absorption health bar turn into red glass panes, indicating that one texture file is used for both bars unlike what happens normally.

How to fix

We can fix this by introducing more individual texture files. We'll need eight in total - they can simply be duplicates of existing files (although dedicated textures would be preferable):

Further notes

The same principle can be used to also fix MC-226845 and MC-226846 (and therefore MC-207252), which I'd strongly recommend doing alongside this ticket. Here's a table of the 16 more textures that would need to be created to fix those issues as well (they follow the exact same pattern):