Where this landed. None of these three shipped as a set. Pairs of a dark and an accent gave way to any colors meeting and mixing on the paper, and the palettes in the app are four sets of a few paints, with their washes beside them.
Every set is a pair, a dark and an accent, and the whole range of that set is the path between them. The ramp on each row is that path, mixed as pigment rather than as light, so blue over yellow arrives at green.
Closest pair is the smallest ΔE between any two inks in the palette; under about 25 they read as the same choice on a phone screen. Travel is the ΔE across a set's own ramp, meaning how far that set can reach. Hue bands counts twelve 30° sectors of the color wheel with at least one saturated ink in them; greys don't count toward covering a hue.
Each set pairs an ink with its opposite, so the path between them crosses the whole wheel and passes through real neutrals. The widest range per set; the most dramatic mixes.
Pairs taken from combinations that actually occur in Japanese painting, kept nearer each other in hue and lower in chroma. Ramps stay inside a family rather than crossing to grey. They are quieter, and closer to how sumi-e holds itself back.
Ten sets instead of eight, chosen to leave no gap on the hue wheel. Some pairs are less opposed as a result, but every region of color is reachable. It is the closest to the range of a full pan set.