ColourTexturesExtensions.swift

import RealityKit

extension ModelEntity {
  func changeMaterial(atIndex index: Int, toColour colour: Color) {
    assert(model?.materials.indices.contains(index) ?? false, "Index out of range")
    model?.materials[index] = SimpleMaterial(color: UIColor(colour), isMetallic: false)
  }
}

extension Entity {
  func addIfModelEntity(models: inout [ModelEntity]) {
    if let modelEntity = self as? ModelEntity {
      models.append(modelEntity)
    }
  }
  
  func getModelEntitiesInDescendants(models: inout [ModelEntity]) {
    self.addIfModelEntity(models: &models)
    for child in self.children {
      child.addIfModelEntity(models: &models)
      child.getModelEntitiesInDescendants(models: &models)
    }
  }
}