Trying to make "paletted_permutations" Atlas in snapshot 24w36a, but unsure why it isn't working.

Messing around with the new armor model features, and wanted to make an atlas that would generate a bunch of wing textures.
Named it elytra_back.json, put it in assets/minecraft/atlases, and put the following inside:
    "sources": [
        {
            "type": "paletted_permutations",
            "textures": [
                "entity/equipment/wings/elytra_back",
                "entity/equipment/wings/elytra_back_outline",
                "item/elytra_back"
            ],
            "palette_key": "trims/color_palettes/trim_palette",
            "permutations": {
                "quartz": "trims/color_palettes/quartz",
                "iron": "trims/color_palettes/iron",
                "gold": "trims/color_palettes/gold",
                "diamond": "trims/color_palettes/diamond",
                "netherite": "trims/color_palettes/netherite",
                "redstone": "trims/color_palettes/redstone",
                "copper": "trims/color_palettes/copper",
                "emerald": "trims/color_palettes/emerald",
                "lapis": "trims/color_palettes/lapis",
                "amethyst": "trims/color_palettes/amethyst"
            }
        }
    ]
}

the three textures were placed into the resource pack in the appropriate location, but referencing minecraft:item/elytra_back_redstone in an item model or minecraft:elytra_back_redstone in an armor model just gives me a missing texture. What am I doing wrong?