It's an awesome hat. Maybe he's got gorgeous, flowing locks which happen to fill out the hat.
I guess they could be black legwarmers, but that doesn't make any more sense considering Hoenn's, like, the warmest region out there. Volcanoes, ashes, constant humidity and open seas...
On a separate worthwhile note, Kanto doesn't really have any spots to grow berries (at least by default - I might be forgetting about incarnations in FRLG or HGSS) and has the most poison-types introduced in a given generation as far as I can remember. In Gen I, Poison is also strong against Bug and vice-versa, and Gen I introduced the most Poison-types by far of any generation. As far as climate and environment goes, it can be assumed that there was possibly a more powerful strain of Poison in the area (hence the extra super-effectiveness), or bare minimum that Kanto has some of the worst pollution rates of the known regions. Even Orre, presumably, was a desert from the beginning. Industrialization and what have you totally killed most of Kanto's ecology, hence why there are very few fertile environments save for short grass. Otherwise it's mostly big cities, mountains and caves.
EDIT: Oh man, BW2 male protag's bag is boss. If it weren't for the doofy hair tucked above the hat he'd by my favorite design for sure.