During my last modeling job the stylelist told me "you should have bought a nude thong," of course I should have but I forgot to put it in my bag at last minute. Usually I am prepared. A model should have a lot of nude colored thongs.
I suggest going to H&M, Target, Wal-Mart, to get them. Sometimes other stores like Forever 21 can be good choices. You don't want to spend a ton on them because they could even get ruined fast at modeling jobs.
Consider airbrush makeup and touchup that goes on for jobs down there, especially for swimwear or bikini shots, your thong could get stained if airbrush makeup is used.
So you don't want to ruin a $20 pair of panties each time.
Also consider that you will need more than one pair and should bring a pair or two pairs to shoots.
Also for even leg modeling jobs, you might have a certain outfit you will need to wear and you do not want your black panty to show through a white skirt you might have to wear. Nude color is best.
You should get thongs. To wear under lingerie you might need to wear for a job, or if the stylelist hands you a thong or undergarments to wear you should protect yourself and wear a thong always underneath!
These are "work" panties.