I honestly think that they should be untradeable. I mean, what's to stop me from making a void force, and then subtract 1 unit from the RGB. There we go, now I have a colour so close to void that I can crash the market with it. Then there's the question of it being no QI. I mean, if every tom, dick, and harry can get themselves a close-enough-to-void/demon/pure etc item, then the current colours would be worthless for those who earn them (there would be no accomplishment, because whitebelts could wear something super close to what a custom belt could wear).
Basically, I love this concept, and I do agree that there should be a change to the way that some joints work so that you can edit the relax of a joint (because I also find it hard to play with joints, because it's hard to tell if it's held or relaxed), but I don't think that this will solve the problem.
I support this idea, but it's execution sounds like bad news bears.