The subspecies [many are now species] were described using morphological data, including coloration, and sometimes reproductive differences. In some cases, geography is very important, as there are similar forms from distinctly distant locations, either due to convergence or to shared ancestry.
Identifying through these details at the very least requires 1) one or more good European field guides, and 2) scientific papers reviewing or describing one or more of the forms [for example,
Salamandra salamandra werneri and
S.s.beshkovi in the Balkans:
http://biozoojournals.ro/nwjz/content/v8n1/nwjz.121102.Vukov.pdf ]. There can still be problems though - many wild-caught animals not only lack place of origin [but will mostly be from Ukraine, due to export bans elsewhere], but need further revisions [the
Salamandra infraimmaculata complex may contain additional species and subspecies].
There is an article on this site, but I don't recall how helpful it is, and I don't have many useful references for European taxa. I do have Jean Raffaelli's recent book, but I have not endeavored to read the
Salamandra chapters [it is in French, in which I am rusty].
In any case, it's not as simple as counting colors and stripes or spots.