In consultation with J, we decided to dye it pink. Given it was this light purple colour initially, I didn't want to make it too murky by trying to overdye it another purple, and I wasn't sure exactly what would happen if I used a blue dye over it. So off to the supermarket for some pink food colouring it was.
I soaked the vest in some cold water with at least a cup of white vinegar in it (sorry, no photo of this step, but if you look through my blog at other photos of me soaking wool and wool garments, it looked exactly like those).
I then put it in the slow cooker with some of the soaking water, a bit more vinegar and some hot water to bring it up to temperature. It is essentially the same process as dyeing wool.
I added lots of pink food colouring (because its actually pretty weak as far as dyes go), and voila, a pretty pink vest with no sign of the marks that were on the front of it.
Have you overdyed anything? Or managed to remove stains or repurpose a garment before?