Overseas profits are reported each turn on the Deal Book. You earn these profits for any resources produced on land you own in a Minor Nation that are sold by that Minor Nation during trade. 

If your Great Power purchases the resources itself, the overseas profits are a refund of the money you paid for them. This refund can reach 100% if you obtain a Minor Nation as a colony.

If another Great Power buys the resources, the money you earn comes from the pockets of your foe.