I've very mixed feelings on this whole thing.
I think the original toning was from being next to acidic paper for some amount of time. Over more time that would damage the card, (Still might because it's not all gone) The process for removing that involves either a bleaching agent or a deacidifier.
Lots of good general info here
http://www.collectorsguide.com/fa/fa010.shtml
Any of that should be disclosed, and should be part of the items history which should be included in any transfer.
But it won't, because of the stigma attached to even appropriate conservation that all gets lumped under the heading of "alteration". That stigma affects value in out hobby, perhaps far more than in others.
So let me ask a different sort of question. The answer matters less than the thinking behind it, although I have a preferred answer.
If I had the card. And posted it here raw asking the question "I have this card that's got fairly mild damage from acid exposure that will only worsen over time eventually destroying it. It's a fairly important and valuable card, and I think it should be deacidified so that it will last another few generations. But I'm concerned about how that will affect the value. What should I do?"
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My preference is for doing the conservation. If it's done professionally there should be no damage, and aside from earlier pictures, no physical indication that it's been done. Without conservation, we as a hobby are essentially condemning some of the best items to a premature destruction.
TPG will probably NEVER be realistically able to work with conservation vs eventual damaging originality as long as they operate the way they have. And as long as genuine conservation is looked down on by the hobby in general.
Nearly every other hobby accepts disclosed conservation/restoration as long as it's done appropriately. Some hobbies ignore some conservation that's not disclosed. Coins- nearly every really bright looking uncirculated silver coin has been cleaned. Other Silver objects- basically have to be polished occasionally to remove tarnish. If it's not brown/black it's been cleaned. Maybe it's time for us to do the same.
And I don't buy the "It's a PSA 7 so it's A PSA 7 and nobody should question that" line. Grades should always be questioned if they seem off.
Steve Birmingham