I've never had beer stone appear "white". My guess is a mineral buildup, possibly the result of hard water.
The one thing apparently not tried is something acidic. Try mixing up a white vinegar & water solution, maybe a cup of vinegar in a quart of water (or a strong Star San solution - doubled, just for grins) pour it in, give it a good swirl, let it sit for awhile, repeat a couple of times, then dump into the next keg and rinse out the first, and see how it looks...
Cheers!
[edit] I just noticed the "lime removal" part. I assume that was something acidic (CLR, perhaps). If that's true, I'm not sure what you're looking at...