Mac, just grab the Religion & Revolution mod from these forums (in fact, R & R even has its own separate forum here!).
Religion & Revolution is the largest, most comprehensive version of Colonization which exists. It adds so many different play options its unimaginable.
Portugal exists as one of the starting nations you can choose to play. There are also two additional ports you can sail to, dozens of added Native tribes, huge and realistic maps of both North and South America, as well as tons of new trade goods you can buy and sell.
If the gaming world at large knew of the R & R mod, and how much it added to Civ4: Colonization, then Civ4: Colonization would quickly become one of the year's biggest sellers on Steam.
It's that good.
Also, it's still being updated, "patched" if you will, right on up to the present day.