The same hormones are responsible for giving pubic and underarm hair
their extra pigment, it's also why they are curly even if your other hair
Honestly, I don't think you should resort to bleach or whatever those creams are, the active ingredient causes cancer. It's not worth it, guys don't care/notice anyway. If they are naked with you and are busy staring at some slightly darker skin, they have bigger problems! Find a guy who isn't a waste of time, at least that's free.