Maybe I’m out on a limb with this. Is it unreasonable to guess that infants coined words for breast and female parent? If you watch a baby anticipating a milk meal or approaching his mother, you’ll see the lips repeating the motion of suckling. If there’s a vocal noise with it, it comes out with an M or B sound. It’s no wonder many babies say “Mama” before they know that’s her name.
Actually, that’s generally considered to be true by linguists, at least in regard to “Mama” (and “Papa”). They suspect this is why the baby-words for mother and father are something like these in the large majority of languages. The reason is that, just as you said, when you vocalize with your mouth closed, you make an “m” sound. When you open it and keep vocalizing, you get an “a”. Papa and Baba (as in Mandarin, for example) are similar - if you close your mouth firmly and “explode” it open with air, you get “b”, and if you stop vocalizing for a moment when you do this, you get “p”.
I’ve never heard any word for breasts, such as “boob”, addressed in this theory. It’s not related to suckling, but rather attention-getting in general. The idea is essentially that baby makes noises, and parent responds, thus reinforcing the effectiveness those particular noises. Basics of language formation, right there.
Victoria’s Secret was started by a man specifically as a place for men to buy underwear they liked as gifts for their wives and girlfriends. Over time the target market shifted.
Bras were available in gaudy colors and fashion prints long before then, however.
I’m thinking white became the bra standard at least partially because because many people do favor having their bra compliment the color of their underpants-- and white panties are sensible for the reasons others have already pointed out.