I've painted my mesh in vertex paint, but I would like to edit the colours in Gimp, then reapply them as a texture and bake back to vertex colours. Is there a way to export just the vertex colours? So it appears as a image file?
First, switch to blender render engine temporarily to bake out the vertex colors to an image (I won't go into the details of how to bake as there are tons of tuts out there for that).
Edit the resulting image in Gimp.
Then setup an image texture in BI and enable bake to vertex color, then bake in "Textures" mode.