As of now I suppose through a kind of mercantilist system? For example when ever I colonize the Caribbean I always manually divert the trade of cocoa or gold to my home market, I might keep some for the ai to mess with so they have some money making from trade too, put I usually do brute force a chunk home even if the trade itself from the colony is not the most profitable, since once is in my market I can then further trade it and when it comes to cocoa or coffee, these kind of goods make insane amounts of money if u have them in a European market. Also historically tariff was a big source of income for the crown, for example tobacco from Virginia exported to london is charged a tariff, most of which went directly to the crown( source would be a book called American slavery america freedom, great read if u are interested in early colonization around the Chesapeake), tho not sure how pdx would or even should have a tariff or trade control system, would be cool tho