Idea that came to me while I was trying to reconcile assumptions I held about UT with DELTARUNE. Basically just the idea that Kris's SOUL isn't Literally the player's avatar (even though it functionally is most of the time). Rather, the player's avatar is a step behind that.

(In writing this I realize that this distinction was Always true in Undertale ["Then it is agreed. You will give me your SOUL"], but my flawed assumption got me thinking about this more, so I'm taking it as a win anyway)

Various character sprites in the 2nd Sanctuary's lighting. To my understanding, the 2nd Sanctuary's effect on color is largely a hue shift. The effect is done at runtime; there aren't separate sprites with different colors. The lighting intensity also undulates slightly.

There's a lot that implies that Kris needs sugar and/or more food in order to sustain themselves without the SOUL. They eat a whole damn pie between Chapters 1/2 (and they must've been up to Something Else besides pie eating during that time, else they wouldn't've been so sleep-deprived the morning of Ch2), have the chocolate milk in Ch 3, and pass out soon after finishing off a glass. Between playing piano, and the lunging, throwing, and whacking shit they do to their SOUL in that chapter, they've gotta be EXHAUSTED by the end of it ('s why they trip on themselves, even after reabsorbing their SOUL).