As a Roblox developer, it is currently impossible to adequately modify the properties of parts, such as their material or their colour, at certain areas of their surface. I think this could be technically done using negative parts, but there isn’t really any other way, and it causes many problems.
Is it considerable to have a new type of negative part that would enable this?
I feel like it’s honestly easier to just have a CSG part where you negate a bit off of each surface. Another option is to add a texture. Overall, there is too little use and a couple of available workarounds that make this feature a bit unnecessary.