Devastation is Red and Blue magic (Pyre is Devastation only, Disintegrate is their primary spender, with both of their only empowered spells being Red (Fire Breath) and Blue (Eternity Surge). In that regard, Flameshaper appeals to the red magic theme, Scalecommander goes with the Blue (Mass Disintegrate) and the Breath.
Augmentation is primarily Black and Bronze themed with limited amounts of red shared with all evokers with their spender being Black, their spec-specific empowered spell being Black, and all of their other abilities aside from Fire Breath and Living Flame are Bronze, including Breath of Eons. That’s why Chronowarden (focus on the Bronze) and Scalecommander (focus on the Black and Breath) are theirs.
Preservation is Green and Bronze themed, which as before pulls Chronowarden in for theirs as a no-brainer and Flameshaper pulls back towards the healing side of Living Flame a la Alexstrasza as to explain how it fits for a healer.