A cut and paste.....
Source location: most palette tangs are collected in the vast waters of the Philippine and Indonesian Islands; these have not proven to be the better specimens. For what it's worth (and it does cost more, and is well justified), Paracanthurus hailing from New Caledonia, Christmas, Fiji and Marshall Islands et al. are superior. How to tell where yours is coming from? There's always taking a gander at your dealer's invoice; and a skilled eye can discern the more robust, better colored specimens from these "other" locales. My advice; pay the extra to get better livestock; encouraging better capture, holding and shipping practices elsewhere.
Color; mentioned here as a criterion to not select by. These fish do change intensity with stress and mood; but quickly and unreliably. Besides, there are subtle to larger color and marking differences with locality and size that are hard to elucidate.