Each card is a zoomed-in view of a single path — the two Sephiroth it joins curving in as half-circles from the top and bottom edges, the path itself the gradient running between them.
Kether is figured in the Monad’s near-white and Malkuth in the deep earth of the four quarters, since neither is a single color in the system; Chokmah takes a soft grey to part it from Kether. All other Sephiroth carry their canonical Cathartes color.