A tiny Blender add-on that exports Wavefront .obj with vertex colors.

Standard OBJ throws vertex colors away. OBJ 2.0 keeps them using the common extended-vertex convention — the color is appended to each vertex line:

v  x y z  r g b

Geometry stays 100% valid OBJ (v / vt / vn / f), so importers that ignore the extra columns still load the mesh, while importers that understand them (e.g. the Affinity engine) pick up the per-vertex color.

1. Download obj2_export.py.
2. Blender → Edit → Preferences → Add-ons → Install… → select the file.
3. Tick OBJ 2.0 — Wavefront export with vertex colors to enable it.

File → Export → OBJ 2.0 — Wavefront + Vertex Colors (.obj)

Options:

The active Color Attribute is used. Both POINT (per-vertex) and CORNER (per-face-corner) domains work — corner colors are averaged to one color per vertex. If the mesh has no color attribute, plain v x y z lines are written.

A normal OBJ, except v lines have three extra numbers — red, green, blue:

# OBJ 2.0 — Wavefront OBJ with per-vertex colors
# vertex lines carry color: v x y z r g b
o Cube
v -1.000000 -1.000000 1.000000 0.901961 0.215686 0.184314
v -1.000000  1.000000 1.000000 0.180392 0.760784 0.298039
...
vt 0.000000 0.000000
vn 0.000000 0.000000 1.000000
f 1/1/1 2/2/1 3/3/1

• Colors default to 0..1 floats (MeshLab / Blender convention). Switch the export option to 0..255 ints if your importer expects bytes.
• A vertex with no color (mesh without a color attribute) is written as the usual v x y z — so you can mix colored and uncolored meshes.

The color columns are optional, so a parser just reads however many floats follow v:

// returns vertex count fields parsed from a "v ..." line
float x, y, z, r = 1, g = 1, b = 1;
int n = sscanf(line, "v %f %f %f %f %f %f", &x, &y, &z, &r, &g, &b);
// n == 3  -> position only (no color, default white)
// n == 6  -> position + RGB

MIT.