Custom item models that use dye tinting will fail to render their tinted faces in certain conditions. Based on my testing, it happens when:

• The item has no "dyed_color" component.
• The item is not a placeable block.
• The "default" color set in the item definition is a positive number.

The attached resource pack contains a simple item model that displays this. It consists of an upper cube that's tinted and a lower cube that isn't.

How to reproduce:

1. Install the provided resource pack
2. Run

   /give @s white_wool[item_model="test:test"]

   This renders correctly.

3. Run

   /give @s stick[item_model="test:test"]

   This does NOT render correctly (only the bottom cube is visible)

4. Run

   /give @s stick[item_model="test:test",minecraft:dyed_color=4208181]

   This renders correctly, even though the defined color is exactly the same as the default on the item definition.

Lastly: If you open up the resource pack and go to "assets/test/items/test.json" and change the default color to be any negative number, everything renders as it should with no issues.

Code analysis

The net.minecraft.client.color.item.Firework#calculate and net.minecraft.client.color.item.Dye#calculate use this.defaultColor without wrapping it in ARGB.opqaque.