Four times it was hinted that Red SOUL trait is an anomaly in some way:
The first time traces all the way back to Undertale, actually, when the Ball Game already set the Red trait as something not only nameless, but also both "above" and aside of the other known six:
Second time was ever since Deltarune first dropped, as we've seen the seven golden flowers only six of which were colored with the SOUL colors and the color Red was missing:
Now we of course know the context for why that is: the Flowerners are connected with the Fallen Humans in Undertale in one way or another but since Chara's SOUL was lost and Frisk lived, getting the Red Human SOUL was never an option here! But with how many layers and subtexts Toby puts at once in the same thing this still fits the pattern nonetheless.
But Chapter 5 provided even more evidence for this! Two of them, in fact!
I do not even necessarily use the flashback scene color-coding to conclude that Patience is Kris' SOUL trait underneath? For example, Toriel is simply color-coded here, without attachment to any concrete SOUL trait!
What does point towards Kris' trait being Patience though is... just their personality, I suppose? It would simply work considering what they are like. But there is a second interesting case that is similar:
Aqua's ribbon is shaped as a heart and we practically see her symbolise recolouring the green heart into red! I could only think of Frisk as potentially referenced character here as Kindness does seem like their more prominent trait! Their true personality during the playing Undertale is defined as all the kindest, pacifist choices you can make!
On the other hand it could be more generic representation of the idea of the color underneath the Red, without attaching it to Kris or Frisk! After all, ALL Flowerners show similarities with Kris, not only Aqua ( x )!
However if I was to choose "true" trait beneath the Red for Chara I'd pick Integrity. Justice doesn't fully apply to them as they are driven by vengeance that is directionless and wished to skew favour in Monsters' favour instead of restoring the balance and Bravery doesn't fully encapsulate their depth and nuance! Meanwhile, they are sure true to their own moral principles to the very end, however skewed, and they are wholeheartedly devoted to the people they've chosen. Funny enough: Aqua did mention that she wanted to be Blue too! If all these snippets do mean anything there is a reference to all three known humans of the Red SOUL!
It makes sense that Red trait stands aside as so far it is the only one proven to be connected with the "divine guidance", ie basically perceiving ours, the Player's, will and working around with it. It also seems that Red trait has the highest amount of Determination in general and sometimes goes hand-in-hand with its golden color. A little strange that it is the part of the full rainbow spectrum chosen to represent the outside element... Would not pink, a literal nonexistent color, pass this theme better?
