Spoiler (click to reveal)
First, Rule 2 notes that "Colonies offer no powers while inactive but the player". Is the colony's field considered a "power" that isn't available when inactive, or do you get the field's income even if the colony is not active? On the one hand, it seems as though the spirit of the activation rules is that you basically gain no benefit from the colony unless you activate it. On the other hand, step 3 in the winter sequence says "Players place gold from every field they control (equal to the gold shown) into their vault", and the player does control the colony, regardless of activation. On the (third?) hand, you can't raid an inactive island site, which supports the idea that the field effectively doesn't exist until it's activated.
Second, as of Rule 8, the (partial) winter sequence is:
7. Activate Colonies
8. Colonies collect
It appears as though step 3 covers ALL fields (including colony fields), while step 8 is when you can choose a goods production or mine site to
robengage in peaceful commerce, and that's done after activation. So, depending on the answer to the first question, this means that either:
a) If inactive fields can't be used, then you can't use a colony's fields during the first winter of the game, but can grab a good or skim mine profits if you activate.
b) If inactive fields CAN be used, then you can use a colony's field to help pay for the activation cost (in addition to the free good or mine money, with activation).
Third, is there any reason to believe that a field upgrade can't be applied to a colony field? The wording seems clear ("any region you control"); the only reason I ask is that it seems pretty strong to increase the field's yield from 2 gold to 6 (or more) in a single upgrade. Especially if you can use it before activation!)