Issue was caused by VBOs using CD_TEXTURE_MCOL for faces colors. This
layer was creating on mesh display (from draw_tface_mapped__set_draw)
in cases there's no such a layer.
If material settings are changing, this layer wasn't updated and old
colors were used.
Fixed by performing an update of this layer in cases it's already
exists. This would give some % of slowdown, but don't think it'll
be dramatically bad.
Would be nice to find a nice way to update such a layer in cases
material is actually changes only, or get completely rid of it/