skin paint

The skin's colour, per vertex, with no engine: the lips and stubble the character builder paints over a body, as numbers an exporter writes out. The skin's material carries one colour (skinAlbedo, from skin-tone's dials); these are RATIOS over it, one per skin vertex, so the drawn colour is material × vertex colour. glTF does exactly that with a vertex colour (COLOR_0 multiplies the base colour), so a character written by skinned-glb with them looks the same in any engine that reads glTF, with no texture to bake.

import { lipTint, stubbleMask, stubbleTint } from 'tosijs-3d/skin-paint'
import { skinAlbedo } from 'tosijs-3d/skin-tone'
const colours = lipTint(skin, lips, tone, redness)              // RGBA per skin vertex
const mask = stubbleMask({ skin: body, normals, vertices: skin.vertices, positions, lips, beard })
stubbleTint(colours, mask, 0.6, skinAlbedo(tone, redness), hairRgb)

• lipTint: toward the lips' own albedo where the pack's lips region says so, feathered at its edge.
• stubbleMask: where stubble grows, measured from a full beard fitted to this body (and a moustache, which the full beard lacks): below the cheeks, not on the lips, and down the front and sides of the neck, fading.
• stubbleTint: the skin there toward a darkened, slightly cool hair colour (short hairs read as a shadow), by an amount (0 clean-shaven).