Almost there but unfortunately this is per UV Islands. This is still a great plug in I am keeping it thanks. I can always duplicate my geo, and fix UVs for required mesh it just adds up a step
I was more interested in applying random vertex colours to geometry with different materials applied. That Way can get ID Maps inside of the same geometry even when they are not loose parts on it. But no luck so far.
I know it’s a dead topic, but if I found it, maybe others will, too. TexTools free add-on is still going strong and can assign separate meshes their own vertex color.