Is there a way to programmatically tint(darken) the material of an Entity that was created in Reality Composer?

Question

From the linked pages below, I've been able to change the color to a solid green. However, I just want to darken the existing material of multiple 3d models each of which have different color schemes.

Their color schemes are based off of a png I've given each model as a physically based material, not sure if this really affects anything big picture. I really do not want have to go into reality composer and make a custom darker color palette for every model...

I would also like the material change respond to input data, not a hard-coded change. I've made a model entity and have been able to change the color manually.

content.add(michelleSceneEntity)

guard let michelleJumpModel = michelleSceneEntity.findEntity(named: "michelle_jump") else { return }
            
let modelEntity = michelleJumpModel.children[0].children[0] as! ModelEntity
            
print(modelEntity)
            
guard let michelleJumpAnimationResource = michelleJumpModel.availableAnimations.first else { return }
let michelleJumpAnimation = try AnimationResource.sequence(with: [michelleJumpAnimationResource.repeat()])
            
let material = SimpleMaterial(color: .green, isMetallic: false)     
modelEntity.model?.materials = [material]
                       
// michelleSceneEntity.model?.materials = [material]           
michelleJumpModel.playAnimation(michelleJumpAnimation.repeat())

Answer 1

Yes, you definitely can programmatically tint a material in RealityKit visionOS app. For that you need a texture file (if you have a USDA file it's not a problem I suppose, however, if you have a USDZ file, read this post to find out how to extract textures from a zero archive).

Here's the code:

import SwiftUI
import RealityKit

struct ContentView : View {
    var material = SimpleMaterial()

    init() {
        material.color.texture = try? .init(.load(named: "diffuse"))
        material.color.tint = .lightGray
    }
    var body: some View {
        RealityView { content in
            if let character1 = try? await Entity(named: "Character") {
                character1.position = [-1.2, 0.0,-3.0]
                content.add(character1)
            }
            if let character2 = try? await Entity(named: "Character") {
                character2.position = [1.2, 0.0,-3.0]
                content.add(character2)
                
                print(character2)   // ModelEntity is "Object_0"
                
                let entity = character2.findEntity(named: "Object_0") as! ModelEntity
                entity.model?.materials = [material]
            }
        }
    }
}