A New hope:
Last night, I was wet-sanding my armor calfs and shins. They had some stains lighter fuel wouldn't remove, plus one shin got some deep scrapes from a fall I took when I tripped on a parked bike. It took 2 bikers to scoop me off the ground.
I wet-sanded the scrapes and buffed and polished the shin back to glossy. I'm fortunate to have a HIPS armor that is very, very thick. About 1/8" I also did the same with the yellowish edges. All it took was a wet-sanding job to remove them. Then, I though: what if the yellow is ALSO sitting on top of the white in my back plate and belt, just like it was seating in the edges I just wet-sanded back to white?
So, I did a test. I wet-sanded a spot of the back plate. What do you know? White underneath!
So, what I have to do is wet-sand the WHOLE back plate and buff/polish it back to gloss. Because of the back's details, I'm going to dread wet-sanding around the gear part and the 2 rectangles. Hopefully, wire wool will help. I'm glad I figured this out. I DIDN'T really want to paint it. Paint scratches, chips, gets dirty, scrapes and only gets worst when more paint is thrown to hide the damages.
I'm taking pics of the process. I though I was just going to fix-up the armor for Halloween weekend, but I'm going all out to actually RESTORE it. I'm undoing all the rivets to have better wet-sanding/polishing reach on all pieces. I'm very positive about the results. I will blog about my process once I'm done. Will post quick updates here, of course.