Answer: Tomatoes ripen from the inside out. On lots of tomatoe varieties, the red color of tomatoes won't form when temperatures are above 86oF. So, if you live where the summers get quite hot, leaving tomatoes on the vine may give them a yellowish orange look. It's probably better to pick them in the pink stage and let them ripen indoors in cooler temperatures.
Tomatoes need warmth, not light, to ripen, so there's no need to put them on a sunny windowsill. Place them out of direct sunlight -- even in a dark cupboard -- where the temperature is 65 to 70F and they will turn red.
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