Hi Brett, what colour are you looking for a lighter yellow ? Not much you can do with the cap as they are thin I'd leave it. DB may be able to send you out a white mix that you can add to the CG to make it lighter.
The only way to lighten the back/sides is to sand it back a bit. I'd use the grit you last used so probably around 320 grit so you don't leave any marks.
I've built one of thse kits with the pre-amp and it sounds great with the stock gear