I am currently working on a project that involves showcasing 3D renders of iron doors using gltf models in three.js. The final result should resemble the image found here: iron door example. I am facing a challenge where I need to selectively change the color of only the frame while keeping the glass pane color intact. How can I accurately identify and modify the color of just the frame without affecting the glass panel's color? Your insights would be greatly appreciated. Thank you.