Honestly, I don't like to see what the boys in my family are wearing at all. ;)
But, my 14 year old WAS wearing boxer briefs for the past couple of years. This summer he decided to switch over to plain cotton boxers.
ETA: by the way... what grade is your son in? If his friends aren't wearing what he is, he will figure it out quickly in the locker room at gym time. If you are concerned that he is mistaken, then don't stock up. Just buy him a few of what he wants, and then wait. He might change his tune, as some of his friends might have changed their preferences since last year....
As for what to do if he still wants the white... well, if he still likes them, he still likes them. You might buy a few packs of other varieties to see if he wants to try them out... he might discover he likes something else better. But if not, why make an issue of it? He's the one wearing them. I wouldn't want my mom making me wear THIS bra vs. THAT one, if the one she liked made me feel uncomfortable, even though SHE liked it better.