very brilliant job.
Is it possible to export obj file with all faces grouped based on their materials. for instance, all faces with color-0 are placed together, and then another color, and ...
something like
g pb-GRP-2609-Color_000
usemtl Color_000
v...
vn ...
vt...
f...

g pb-GRP-2670-Color_000
usemtl Color_000
v...
vn ...
vt...
f...

#//all other faces with Color_000 ...
#then another color, color_001 for instance, and all the faces with color _001 are placed together

g pb-GRP-2639-Color_001
usemtl Color_001
v...
vn ...
vt...
f...

#//other colors ...

That can be useful for some applications, for instance, using snappyHexMesh in OpenFOAM for general CFD(computational fluid dynamics) applications.
There should not be too much job it think, but it will facultate a large group of openfoam users. Would it be possible for you to add such a functionality in your next release? Thank you very much.
Best Regards, Junwei