You often hear gardeners argue about when is the best time to pick tomatoes.
Tomatoes are considered to be vine ripe if they are at the "breaker stage" of maturity when they are picked. Tomatoes are at the breaker stage when pink color first becomes noticeable. These tomatoes are physiologically mature and will develop red color naturally. When tomatoes are picked at the breaker stage they can be handled and shipped with less damage than those that are more mature when picked.
Most home gardeners handle their tomatoes carefully and don't have to be worried about shipping damage. Therefore, there is no reason not to wait until the tomato is a little past the breaker stage before picking. That way, you can eat the tomato right off the vine. It's good to know, though, that you can harvest at the breaker stage should you need to take or ship some tomatoes to a friend who doesn't live close by. Just remind the friend to spread the tomatoes out so they can continue turning if they have not yet reached the stage he prefers.
For shipping, many tomatoes are picked at the mature green stage. At this stage there is jelly-like material in all the internal cavities of the tomato. Seeds cannot be cut by a sharp knife when slicing the fruit. Most fruit picked at this stage are then exposed to ethylene-based gases to complete the ripening process. This allows the fruit to be picked, packed and shipped with the least amount of damage and to have the longest shelf life.
It is the source of much controversy whether a mature green tomato tastes as good as a vine ripe tomato when both are fully colored. Some folks believe that the only real tomato is one picked red off the vine, while others think that tomatoes picked green and ripened in shipping are just as good. There is no doubt that this controversy will continue as long as there are tomatoes to be picked. Probably the only agreeable point between debaters is that the green version is quite good fried. If you want your tomatoes to be red when you get them, I suggest you put a few plants out on the patio and pick your own as you need them.