A few addons that have Proxy Color Tool support. Should give you a good idea of what is possible with it.

https://steamproxy.net/sharedfiles/filedetails/?id=2075396899
https://steamproxy.net/sharedfiles/filedetails/?id=2113101537
https://steamproxy.net/sharedfiles/filedetails/?id=2071672800
**any GTAV vehicle of mine will support this tool as well**



Some things I've noticed:
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I like how with the Audi RS6, the model utilizes the proxy color tool for interior coloring and the color tool for the body panels. This is a neat idea that makes the proxy color tool not *needed* but allows both tools to be used together without conflicting/coloring each other.

With the Ford Taurus, the proxy color tool is utilized for coloring the brake pads, hubcaps, and calipers. While it is a similar setup to how the Audi was done, using the proxy color tool for only extra bits and not the body panels themselves, the color tool will tint/overlay proxy color tool colors and offset them.
The Audi definitely did better when adding proxy color tool support but I don't think the color tool and proxy color tool conflict on purpose. It is a cop car with a livery so it didn't really need colored body panels (until you change the skin from 0 to 1).

The splatoon hairstyles utilize this tool in a different way than I thought this tool would be used. While each material on the hair props have only one color slot each, I am sure with some cool vmt magic you could put multiple color slots on one material. I am not that knowledgeable with vmt files and proxies so I don't know of any cool tricks to utilize or better make this tool but I am sure there are people out there that can pull off similar effects to the splatoon hair colors with only one material.
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This discussion is not meant to be a complete list of all addons that support the tool, but if you want to comment an addon that supports this tool below you may.