Here is my fist gizmo for Nuke: Multi Color ID combines the RenderID and Coverage pass from the VRay for Maya Render Element.
It was a good experience to recreate it in Nuke and it handles a lot quicker in Nuke than in Fusion. Feel free to use! Download here:
Practical information: I am using Adapative DMC sampling and Linear Workflow. This Gizmo is Nuke 6 and above.
If you like it or use it a lot drop me a line. It is always nice to hear when people are using your free stuff.