The VRCFury setup is relatively simple

Scene Setup

Find the Rainbow Prefab in the ‘RuneFox/Rainbow/_Prefabs’ folder and drag it onto your avatar so that it becomes a child object of the avatar.

If you need to scale the system only scale the Parent Rainbow System Gameobject. Try not to scale any of the gameobjects inside the prefab as that may result in undefined behavior.

Setting up the Alternate Position Target

This position is where the Rainbow will appear when using the Alternate Position Toggle in the menu. Mainly used for when you’re in Desktop. Simply find the AlternatePositionTarget GameObject and move it to where you want it. The rainbow guide should be currently parented to it to show where the rainbow will be when it is activated in this position.

That is all that is needed for the VRCFury setup of the Rainbow. You should be able to upload the avatar and use it in-game.