A friend and i were changing to go swimming and i was shocked when she took her bra off. You could see the outline -for lack out a better word- where her bra was. It left marks in her skin where the band and cups were. I think the bra she was wearing was too small but she said all her bras leave marks like that. The marks quickly went away but still. Does this happen to anyone else?
Yes this is normal. Your band needs to be snug enough to actually support your breasts so it's normal that something that presses into your skin a little bit will leave marks. It's similar to socks or underwear leaving slight marks but a bra's will be a little more noticeable because it's a bigger area and because it supports weight/may be a bit tighter.
Sometimes they do. She might be wearing a bra that's fastened too tight for her frame. My underwire leaves dark marks on my skin but it goes away. I have heavy boobs so I can't really adjust them much to make a difference without sacrificing support.
When i lived in australia, i visited many beaches in bikini and that left my bra portion on of my breast skin lighter than rest of the skin. once i moved to my university room, i started remaining topless and my skin tone is fairly equalized.