Five of Eternity II's 22 colors appear only along the border ring, each on exactly 24 edges, never once in the interior. A structural split that shapes how every solver treats the frame.
deterministic — reproduces byte-for-byte
just research-rare-color-geographyThe 22 colors don't play equal roles. Sort them by where their edges sit and they split into two clean classes: five rare colors fenced off to the border, and seventeen common colors that do almost all their work inside the board.
Pick one of the five rare colors and watch the board: all 24 of its edges light up around the frame ring, and the 14×14 interior stays completely blank. Switch to a common color and the interior fills instead. That empty middle, for every rare color, is the whole finding.
Every one of this colour's edges sits on the frame ring. Not a single one appears in the 14×14 interior — that empty middle is the whole finding.
The split itself is structural, not a defensive trick. Because the outer rim is solid grey, every border piece keeps its grey edge facing out, so its coloured edges only ever meet other border edges or the interior: the border and interior colours live in separate pools no matter what. The five border colours read as "rare" simply because there are far fewer border edges to colour, and they could be relabelled to any five values (even reusing interior ones) without changing the puzzle at all. (See the design note on why, with thanks to Vasily V. on the groups.io list for the correction.)
What is real, and what matters for solving, is the consequence: the 14×14 interior is left to seventeen common colours with no rare, highly-constraining signal anywhere in it, which is a large part of why interior search has so little to grip. The border, where the colour pool is small and matches are tight, is correspondingly the part every strong board gets essentially perfect. Eternity II's colour counts were balanced to remove the statistical handholds that sank Eternity I; this geography is where you feel the result.