In Amia, True Seeing doesn't pierce shapeshifts that come from racial or class abilities, just so they aren't trounced by a level 7 spell that's so easily acquired. Which, given how truly easy it is to just get a Lesser Robe of Eyes, I agree with entirely.

As for in PnP. Check out the description of both Wild Shape and True Seeing. Wild Shape acts as Polymorph Self, barring a few notes (none of said notes refer to it being immune to piercing by True Seeing), whereas True Seeing will spot everything for what it truly is; even dopplegangers who get polymorphs as a racial trait. Polymorph Self also has the notation that they assume their original form upon being slain.

Masters of the Wild (the 3.0 Shifter book) doesn't actually state that they lack a true form, merely that it's a perception that they don't (IE, most would have the IC perspective that 'Hey, I'm so good at shifting, no form is 'true' to me anymore'). I don't have the exact wording on me (I quoted it somewhere else on these forums, though), sadly, as the book's been loaned out.

Some time back, the question whether True Seeing can detect shapechanged individuals came up. We discussed it, and came to the following conclusion, which isn't really different from the custom on Amia:


True Seeing does see through the following:

The spell "Polymorph"
The spell "Shapechange"
All magical illusions and other shapechanging spells


True seeing does not see through the following:

The Druid "Wild Shape" and "Elemental Shape" as well as additional shapes like Dragon Shape
The Shifter "Greater Wildshape" and "Humanoid Shape" feats
The "Thousand Faces" ability, attainable with a widget


To put it in simple OOC terms, spells are detectable whereas feats are not.

The first sentence:

"In Amia, True Seeing doesn't pierce shapeshifts that come from racial or class abilities"

Seems fairly concrete to me in preventing True Seeing from seeing through either of those.

*Po-tee-weet?*