The colors on the volume cover are strange. Livet apparently wears not just a golden suit of armor, but also a golden cloak to go along with it. Or is it supposed to be a yellow cloak and Nakaba just used the exact same shade for both the cloak and the armor? Either way it's ugly, but the others look okay. Nakaba apparently decided to switch from knights with colored armor to knights with colored accessories like capes and hats. I wonder if they still follow the color naming scheme? In that case Mortlach would probably be green, Tomintoul blue, Rosebank pink, Glenesk ultramarine, Lochranza white, Brackla orange and Livet presumably yellow/gold or some shade of red(perhaps scarlet or ruby) if we go by the hat. I would expect the green and white knights to be stronger than this, but it's not totally out of the question.
Regarding the Green Knight, this is a total crackpot theory, but I've considered the possibility that Nakaba may have decided to save him for later due to his relation to Gawain. For example, let's say there used to be a Green Knight in Camelot but they disappeared/died and were replaced by some other color. Later down the line some Chaos shenanigans happen and he resurfaces with a huge power boost that makes him a suitable endgame enemy for Gawain.
I will say that a potential problem with this idea is that Anne's mom seemed to be one of Camelot's oldest knights alongside Varghese, Ironside and Pellegarde, so a candidate for one of the primary colors. I strongly feel like she'll come back in some form eventually, which might overlap too much with this Green Knight scenario. I guess she could even be the Green Knight if not for the fact that she has to be an enemy for Anne.
Something that intrigued me about the antler knight is that face and chest are completely shaded even though the knight next to him is totally visible. It's like there's just a void where the antler knight's body should be. This gave me the idea that maybe he is just an empty suit of armor, which would sort of fit the story of Gawain beheading the Green Knight and the knight just reattaching his head afterwards like it was nothing.
As for Jericho, in the Grudge of Edinburgh trailer her armor was grey with a teal visor. I guess you could spin that as blue, especially if the CKs' colors are now determined by their accessories, but I feel like grey would be a more likely candidate for her color.