For all of the tomato's associations with summer, the green tomato seems like much more a seasonal floater. Perhaps that is because green tomatoes are there in the spring as the fruit develops. They also hang on to vine in the fall when it is past its peak.
Calling something a "green" tomato lacks a bit of precision in this day and age when you can easily find tomatoes of every hue. We've grown Green Zebra in the past, which is a common heirloom that is green, if a bit yellow, when it is ripe. At the other end of the spectrum, every tomato starts off green, regardless of the variety. As they mature, the green lightens to a jade color. Once the fruit has reached its eventual size, it begins to show flashes of its eventual shade starting around the bottom of the fruit.
We are big fans of picking tomatoes just as we see flecks of its mature color. Much longer, and we run the risk of attracting the attention of birds, which too often will avail themselves to a sample of that prized fruit you've been waiting to try. Tomatoes are also vulnerable to splitting at this stage when there is too much or too little rain. So, we simply bring them in and leave them on the windowsill or on a tray to ripen. Tomatoes picked this way have no difference in flavor of ones left longer. In addition to bettering your chances against birds and splitting, they also have smaller seeds and are thus more enjoyable to eat.
Tomatoes picked even younger will ripen just fine indoors too. Each fall, a few nights before our first frost is forecast, we will pull any remaining tomato plants up and fill up the windowsill, leaving the rest of fruits hanging upside down in the basement, still on the vine. They slowly ripen on their own schedule, as though they are outside. It is not unheard of for us to continue slicing tomatoes into January.
There's no need to wait for tomatoes to be entirely ripe to use them though. The Italians even prefer to use them when they are slightly under-ripe, as their crunchiness and acidity is lovely in a green salad. That might take a Southerner some getting used to, but we are all familiar with the fried green tomato. We'll post a recipe for these very soon.