That's a complex question, because there is some disagreement about whether panthers are all one species, several sub-species, or even several species.
E.g.
The Panther Chameleon Is Actually 11 Distinct Species
Photos: 11 Colorful Chameleons of Madagascar
Yet there are still ~30+ (depending on the source) '
locales', which to my understanding are supposed to be all of the
same species—like dog or cat breeds.
Going back to the original question, what does the breeder say?
The only other way I'm aware of is comparing the chameleon in question against photos of various locales. However, while some locales can be fairly consistent (colors & patterns), others can be extremely varied, e.g. these three are
all 'ambilobe' panther chameleons:
View attachment 312877View attachment 312878View attachment 312879
Here is
the list from MADCHAM.DE