TUTORIAL >>> Sketchbook X-Wing break down

Jeff -
In image #6, what’s the reason for the color swatches you painted above the main illustration, with color reference codes? Do you use those like a painter’s palette and sample from them to select colors?
I’m still working on ideal workflow in SBP on iPad Pro, but don’t do work finished to this level, mostly 10-15 min sketches.
This is super hot.

thanks.