@BestBoy -- I don't know how much "tan = poor" enters the equation in modern Japan. It wasn't something I ever heard of when I lived in Japan, though I was aware of how the light-skinned look was considered youthful while the more tanned look was older. (All of the middle-age guys I worked with had darker skin, while the girls in the office and younger guys did not.)
This chapter was all about ganguro, which had nothing to do with being poor. Ganguro were rich Japanese girls who were saying "F-U!" to the expected roles for women in Japanese society. Young women were expected to have light-toned skin, silky dark hair, and more natural makeup. Ganguro's went for dark skin, bleach-blonde hair, and ugly makeup. Futaba's fear is two-fold -- 1) she'll be branded as a trouble maker and thus get discriminated against when it comes to job opportunities or the like (because you either tow the line and conform, or you aren't going anywhere) and 2) she doesn't want to give her senpai fodder to make fun of her. She fails at #2, and her friend is telling her not to worry about #1.