Also - if the bright blue figure is possibly Syl, with brighter blue skin than any known human population, do we think the Siah Aimians might be descended from honorspren? In a similar vein to how the light blue Natanatans are thought to come from human/Aimian mixing? They do act very spren-like, with the shapeshifting and the reverse shadow/Cognitive realm connection.
I like the proposal earlier that 5th ideal Radiant spren can manifest fully in the physical realm - could give some credence to this.