HOW IT IS ORGANISED

Four independent test cases, one per property. Each case is a matched PAIR:

  rcbug:uv_anim_entity        rcbug:uv_anim_item
  rcbug:overlay_color_entity  rcbug:overlay_color_item
  rcbug:is_hurt_color_entity  rcbug:is_hurt_color_item
  rcbug:on_fire_color_entity  rcbug:on_fire_color_item

Within a pair the entity and the attachable are identical in every respect that
matters. They share:

  the same model      geometry.rcbug.test, from models/entity/test.geo.json
  the same texture
  the same material   rcbug_color:entity, or rcbug_uv:entity for the uv_anim
                      case, both modelled on vanilla (see NOTES)
  the same render controller body, duplicated under two ids

Each pair's controller carries exactly ONE of the properties, so a failure
cannot be blamed on interaction between them:

  uv_anim        "uv_anim": { "offset": [0, "math.mod(math.floor(query.life_time), 4) / 4"],
                              "scale":  [1, 0.25] }
  overlay_color  "overlay_color": { "r": 0, "g": 0, "b": 1, "a": 0.6 }
  is_hurt_color  "is_hurt_color": { "r": 1, "g": 0, "b": 0, "a": 0.8 }
  on_fire_color  "on_fire_color": { "r": 1, "g": 0.4, "b": 0, "a": 0.8 }

The ONLY difference within a pair is that one is drawn as an entity and the
other as an attachable.

STEPS

  1. Apply both packs to a world. Creative mode is easiest.
  2. Spawn the entity for the case you are testing, with its spawn egg.
  3. Give yourself the matching item and hold it. All items are in the
     Equipment tab.
  4. Stand so the entity and your held item are both on screen.

WHAT EACH CASE SHOULD SHOW

  uv_anim        The texture is four solid colour bands. The entity cycles
                 red -> green -> blue -> yellow, one band per second.
                 The attachable stays on red forever.

  overlay_color  The texture is neutral grey. The entity is tinted blue.
                 The attachable stays grey.


  is_hurt_color  Damage the entity:
                   /damage @e[type=rcbug:is_hurt_color_entity] 1
                 It flashes red. Then take damage yourself while holding the
                 matching item: the item does not flash. (which can be understandable)

  on_fire_color  Set the entity alight with flint and steel. It tints orange.
                 Then set yourself alight while holding the matching item: the
                 item does not tint. (which can be understandable)

ACTUAL RESULT

In every pair the entity honours the property and the attachable ignores it
completely.

NOTES

  - The materials are modelled directly on vanilla rather than invented:

      rcbug_color:entity  {}                          like vanilla creeper:entity
      rcbug_uv:entity     +defines USE_UV_ANIM        like vanilla experience_orb:entity

    `entity` already carries USE_OVERLAY, which is what overlay_color,
    is_hurt_color and on_fire_color need - vanilla's creeper adds no defines at
    all and its overlay_color works. USE_SKINNING is deliberately NOT added:
    entity_static declares it as a VARIANT the engine selects when the geometry
    has bones, and no vanilla mob material adds it by hand.

  - `color` is deliberately NOT included, having been tested and dropped. It is
    not a general render controller tint: the only two controllers in vanilla
    that use it are the horse's, whose material resolves to ALPHA_TEST,
    COLOR_SECOND_TEXTURE, USE_MULTITEXTURE, USE_OVERLAY, and whose value comes
    from query.armor_color_slot - the engine-side plumbing for dyed horse
    armour. Reproducing that material and its three texture slots exactly, a
    constant `color` still does nothing on an ENTITY, so there is no working
    baseline to compare an attachable against. Player leather armour does not
    use `color` either. Including it would have meant shipping a case whose
    control does not work.