I think I don’t follow you, but I don’t even care about formulae or graphs in a user interface. I just seek results: how do you remove color (desaturate) black? 
Again, how do you increase saturation of white, or an already saturated channel? I don’t mind what a user interface pretends to do. It simply can’t do that.
How do you increase 70 to a channel that already has a value of 254 (clipping at 255)?
How do you remove 125 from pure black (0,0,0)?
I think it’s not what somebody say here, but what could be done or not. It doesn’t matter what a user interface makes you to believe.