I've found that seeking out replacement levers that already have decent condition white hoods is the way to go. Typically they've set me back anywhere from $15-25, which to me is perfectly acceptable if I've just gotta have white hoods.

The auction site and co-op are good for this. I once noticed a bike on CL with white hoods that just didn't work with the rest of the bike. I offered him a pair of black 105 levers plus ten bucks for his white ones, talking up the finished look and how it'd help his sale. Done deal. I got my white 105s, he sold his bike, win-win!

They can be found. But it ain't easy.