By selecting all materials, wishing to have a small script or tool to run with auto Material ID numbers.
With many materials its hard to give one by one. I ma sure it will be time saving tool.
Thanks.
Can’t you achieve this auto result by just selecting ID and then material in the drop down in the multipass settings? That randomly applies a different colour on every material or object if you prefer or both.
Seems like a bug to me!
Unique material ID 
Yes that would be nice. Some variation can be achieved with the variance shader but it would be great if corona had its own native one like Max version seems to have.
What would be great is to have it vary by connected poly sets - so for example if we have a tree with a single leaf material and a single object for all the leaf polys corona would look for all the connected polys (a full single leaf) and give that an ID and maybe group a bunch together randomly so we could have say 5 different variations / leaf colours. I think Vray can do this now.