I think it could have some connection to Demon Kings, like we saw with Tot Musica in Film Red.
https://onepiece.fandom.com/wiki/Tot_Musica
On the surface, "Color of the Supreme King" can come across as...poorly translated Japanese gibberish, frankly. It's a bunch of words that don't really obviously have an obvious meaning together.
But, let's break this down a little.
The Japanese word being used is Haoshoku (覇王色) for "Supreme King Color".
https://onepiece.fandom.com/wiki/Haki/Supreme_King_Haki
Of the three characters being used "Color" (Iro) (色) is probably the most interesting.
https://en.wiktionary.org/wiki/色
It can literally mean the color of something. But, it can also mean a mood or emotion. And, interestingly, it can also have connections to a form of romantic love.
So, "Color" could literally mean "color". Or it might be something like "Personality" or "Attitude". "The Nature of the Supreme King". Using CoC may make your personality similar to the Original Supreme King, or something along those lines.
So, "color" is important for some reason. What IS the color of Haki? It's black. Armament Haki turns your skin black. Haki lightning is usually shown as black. The only place it isn't shown to be black is the anime, which is probably using other colors to make things flashier.
So...WHY is the "Color of the Supreme King" black? Well, black is a interesting color in Japan. It can be used to symbolize mourning and grief. But, it's also a color symbolizing masculinity and sophistication and maturity. And it can also symbolize mystery or the unkown. It was also used to represent the lowest ranks of Japan's hierachy in the feudal era, opposite the color purple reserved for royals. In this system it had the virtue of "Greater Knowledge".
https://sakura.co/blog/black-in-japanese-colors-and-more-traditional-meanings
https://kaitojapandesign.com/blogs/...se-culture/colors-in-japanese-chinese-culture
https://en.wikipedia.org/wiki/Twelve_Level_Cap_and_Rank_System
So...there's a pretty large variety of meanings that Oda could be pulling from. And he might be mixing various inspirations together here.
So, here's what I think it could mean.
Back in Chapter 1162, Saturn mentioned that he was worried that all the fighting between different strong Haki-users could cause "something else to be unleashed". I think this could be the birth of a new Demon King, like Tot Musica.
(Chapter 1162)
I've talked a little about it before. But, I think it's possible that Devil Fruits, Klaubatermann, Demon Kings and Gods could all form from very similar processes.
https://worstgen.alwaysdata.net/for...ncident-was-a-singularity.73794/#post-6378324
Bringing this back to Demon Kings. I do wonder what the difference is between Demon Kings and "Gods" like Nika? Again, is it just being formed from positive or negative emotions or wishes, or is it something else? Can "Gods" only be formed by the purer "Dream Energy", while "Demon Kings" can form in other ways? Are they basically two factions of the same "species", as it were? Different cultures just calling them different things?
If we take my idea about the how Demon Kings are formed versus how Devil Fruits are formed into account, I think it could work a little something like this.
Devil Fruits are formed from weak people's wishes that they regret having unfulfilled. Dreams that want to live on.
Demon Kings are formed from strong people's hatred and disagreement with each other. Dreams that clash and grind against each other.
But, the Gods are formed when strong people all have the same dream and work together. Dreams that a group of people help grow and nurture together. A bunch of strong people, working together towards a common goal, creating a spirit that will help their "wish" come true. Like the Strawhats all working together to help Luffy become the Pirate King.
Kind of like a klaubatermann of a ship being formed from the love of the crew for that ship, now that I think about it. It'd just be the difference between a "household god" of a individual family and a "major god" of a region or of a concept. Klaubaterman may be related to the "Gods" in some form. Hmm...
Think of it like...dairy products, I guess. Dreams are our "milk". But, depending on how you treat and USE that "milk", you can make a variety of different "foods" out of that same original product. You can freeze it (not allow someone to live their dream) and make ice cream (Devil Fruits). You can churn it (expose it to Haki) and make butter (Demon Kings). You can let bacteria digest it (work with others) and make yogurt (klaubatermann). Or you can let it age and let it become cheese (Gods).
Think about it for a second.
The Merry's Klabautermann appeared to be black colored, from what little we've seen of it. (Although, it was...orange in the "Episode of Merry" special, so that kind of goes against my theory. But, maybe the anime staff didn't know?)
(Chapter 351)
(Episode of Merry)
Imu seems to be black colored, if that isn't just a silhouette.
(Chapter 1084)
Even Nika, from what we've seen of them, appears to be black colored.
(Chapter 1175)
These might not just be "silhouettes". This may be a pattern. "Spiritual entities" in this world may all just be black colored. Possibly because they're all "born" from Haki and Dreams.
So, when someone is using "The Color of the Supreme King" that MAY be a sign that they are ready to "give birth" to one of these "Spiritual Entities". CoC may be a sign that their will may be ready to manifest separately from themselves. Think of it like...being ready to form your own Stand in Jojo's Bizarre Adventure.
CoC may actually be about trying to create a true "Supreme King". It's about breeding your own God into this world. Like trying to breed a perfect Chao in the Sonic games. Using your dreams as fuel to create a God that can help make your dream come true. Kind of cyclical when you think about it like that.
It kind of depends on if the Gods are separate entities from the people they're created from, or if they're basically ascended humans, I guess. It's just that 3 out of the 4 of these "spiritual entities" are separate from their "dreamers". Devil Fruits, Demon Kings, and Klaubatermann are all their own entities. I'm just not totally sure if the "Gods" will turn out to be the same, or existing humans who gained extremely strong abilities. This could be a metaphorical or a literal "birth", depending on which way Oda goes with it.
So, yes, this means, according to this theory...that you use your CoC in order to create life. You may all giggle like schoolchildren...NOW! (Don't tell me that isn't something Oda wouldn't do!)
Alternately, it could just be because of Nika. It's "The Color of the Supreme King" because Nika was black colored. Someone who is able to use CoC is using abilities similar to what Nika had. Or has the qualifications to hold the title that Nika once held. They have the right "attitude" to be a candidate for the new "God" of this World.
But, if things go wrong, it could also create a Demon King. So, maybe eventually, we'll see "The Color of the Supreme DEMON King"!
...Or maybe I've gone completely off the rails with all this. But, I do have a feeling that "The Color of the Supreme King" could tie into the creation of Demon Kings and Gods in this story. Time will tell.