The rendered nucleus fill (#rrggbb), or null for a blank cell — the color
the raster engine samples and compares (§6.3). A fingerprint-middle cell's
nucleus is the neutralised entviz background.
The cell's 24-bit surround pattern (the fingerprint token's quant, =
data-surround-bits); 0 for a blank cell. Geometry-independent per token, so
it gives a strong self-consistency check when comparing two entvizes.
The cell's token text, or null for a blank cell.
A >512-bit input's neutralised Crockford "fingerprint-middle" cell.