Change The Color of a Mesh Without Affecting a Specifically Textured Part of the Mesh

I’ve been trying to make a door in blender where the door knob stays yellow and then I can import it into roblox and then change the color of the door while keeping the door knob the same color. Is this even possible?

I’ve tried to look it up on the forums and on youtube but I havn’t been able to find anything that will help. I want the door to be one part so its easier to code the door opening and closing and so the game has less parts in it then it needs to have. I have tried UV Unwrapping the door knob part of the door and then putting the color on yellow and then assining a new material for the door part but when i import it into roblox the door has the grid on it of all the colors but the door knob is the correct color.

Here’s the Door In Blender:

And Here’s the Door In Roblox: