Testing discovered MC-262515.

The bug

The texture which is displayed over the screen when inside of a nether portal is determined by what the "particle" texture is set to in the block's model.

As the screen overlay is not a particle, this is unintuitive. It also forbids giving the overlay texture a different texture from the particles. This is much the same as MC-240042.

How to reproduce

1. Download and apply the attached resource pack
2. Optionally inspect the model files in the resource pack to confirm what textures are referenced
3. Break a nether portal to check what particles the portal blocks create when broken
4. Enter a nether portal (in Survival mode)

Expected results

The screen overlay texture would still look like the normal nether portal texture.

Actual results

One of the debug textures is displayed instead.

How to fix

A simple fix for this would be for model files to also include an "overlay" texture parameter, similar to "particle". This texture would be used for displaying screen overlays associated with the block (inside a nether portal, suffocation, when on fire, etc.) and would be independently customizable from particles.

Hardcoding the nether portal texture as the overlay would be undesirable.