Yuna's eyes

[BG-57]

Presumably if the swirling green eyes were widely known as the hallmark of Al Bhed, then anyone of that descent could be easily identified (racial profiling anyone?), which may explain the goggle business.

Unfortunately, since mostly Al Bhed seem to wear goggles, they are still easy to pick out, so they've effectively hidden one badge under another.

That would explain how Wakka could be clueless that Rikku was Al Bhed and even more that Yuna was half Al Bhed.

On a side note, the Al Bhed we get to know well (Rikku, Rin, Brother, Cid) tend to forgo hiding under goggles. Maybe we would find it harder to identify with characters we can't see the eyes of?