I think to wear a thong with white pants depends on what you want people to see... either a nude coloured thong if i don't want it to show, or a bright coloured one if i'm feeling like showing it. in any case, i won't wear a white thong under white pants since that'll just look foolish -- as if you're trying to hide that you're wearing a thong, but white underwear will almost always show through (esp. under thinner fabrics). if i want it to be visible, might as well go with the brightest colour.