Vertex colour is now chosen from the true, unrounded surface height and faded
between adjacent materials across a tunable band, instead of switching at one
rounded integer depth. This removes the horizontal contour banding.
Colour path only: density field, Marching Cubes interpolation/welding, chunk
dimensions, the .dat contract and all road logic are untouched. BlockID
classification is unchanged and still drives non-visual use.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
