Now, the Shetland Islands and Fair Isle, where this brand of knitting was concocted or perfected, is on a similar lattitude to Alaska. And for sure it was developed in a world that was lit only by fire, right? In wintertime knitters were sitting by a peat-burning fireplace, an oil or a kerosene lamp. Less light even than all the bulbs and tubes burning in my house. (And I still can't see the colors properly except in daylight.)
Here comes the Blinding Insight, which I'm sure has occurred to you by now, too: The majority of knitting time would have been in the winter when there were fewer outdoor chores to do. Wouldn't it have been a natural thing to limit your colorwork to two per row, a Dark and a Light, so that you could carry on without daylight and have fewer chances for mistakes?
This idea is suddenly so totally obvious that I don't want to check knitting histories to find out who has already thought of it. I don't care. It came to me independently, as it did to the first fair isle knitters (probably), and I like to feel a kinship with them as they sat before the fire, chatting, telling and hearing stories, or singing, and I sit before the dvd film with an electric lamp on my work, while we all create a dance of color in wool.
PS: Scandinavian knitting. Two colors, dark and light. Think about it.
PPS: I'm now halfway through the second pattern repeat!