When you are dragging a ravager spawn egg, it's color will become the mask spawn egg. Apparently the ravager.entity.json file uses "base_color" and "overlay_color" instead of "texture" and "texture_index". Here's an comparison between a ravager's spawn egg and a vindicator's spawn egg. This is seen in the ravager.entity.json file.
ravager.entity.json
"geometry": {
"default": "geometry.ravager"
},
"render_controllers": [
"controller.render.ravager"
],
"spawn_egg": {
"base_color": "#757470",
"overlay_color": "#5b5049"
vindicator.entity.json
"geometry": { "default": "geometry.vindicator.v1.8" },
"spawn_egg": {
"texture": "spawn_egg",
"texture_index": 39
adding your code notes to MCPE-42485 with credit