Devil mask progression appears to function through what I'd call "parasitic actualization". Devils begin as pure chaos, but are bound into the hard limits of humanity through masks. However, this does not itself grant any true humanity, only the appearance thereof. This is why the lowest mask, pale, is alien and nonverbal.
Yet pale masks are not truly "low". We see devils of various competence and wealth all over the mask spectrum. There's two pale devils in the vaultrobbing crew, even.
Rather, devils appear to progress whenever they use contracts to steal fundamental things from humans. Note the contrast with the nonverbal white devils and the blue devils who have the "gift of tongues". When a devil decides to to the stereotypical thing and "steal a human's soul", or their voice, or their mind, or their essence, when the devil starts to see humans as "meat", they make a cognitive leap. They absorb some of that humanity. The pale devil ceases to be pure chaos contained only by the aesthetic form of humanity, and becomes, in some small way, more humanlike. They become blue.
And so they progress, becoming more humanlike and gathering wider patterns of humanity. Abbadon hasn't explored it yet, but my bet is that humanity is like an addiction to devils, not to mention it makes a convenient Dark Souls reference. They thirst for more and so make more contracts to get more access to understanding of humanity, even if they do not consciously realize this or act in any way humane (Oscar...).
This continues, withering and growing in a humanity they do not know or understand, until they become gold devils, and they hit a wall. They've absorbed so much, taken so many contracts, that there is nothing left to gather from the world. The only thing to do, the only way to progress further, is to hit self-actualization and gain a true identity not cribbed or stolen from humans. This is why ebon devils are not made by contract, and why they choose their own names.
Princess is able to go back with relative ease because she still has most everything that made Vladok within her. The binding names are holding back a tidalwave of wisdom and power. And so they hold, for the most part, for now. But eventually the Jagermeister will be dried up and the Princess will come undone, restoring...something. Not necessarily Vladok.
Cio has hit a form of metastability as a blue devil. Her desire to be not just human but humane has arrested her inherent nature's assault on the binding names. She accepts "Cio", prefers it even. It is an accomplishment far more meaningful than it seems, particularly given that she was otherwise in short order gearing up for a jump from blue to ebon until nuclear lesbian flames intervened.