Being a bride myself, I've been a little concerned with things showing through my white dress (like undergarments). White stands out like a lamp. Nude shows. Something blue definitely shows. But red doesn't.
It sounds insane. It sounds really insane. But for some reason, red disappears under white. So if you're a bride, and you want to wear something under your dress that doesn't show, go for a pair of sassy red underwear. After all, who doesn't feel sexy in red?