3 Answers

Only a temperature of around 70 degrees F will enable green tomatoes on the vine to turn red. However, you can always pick the green tomatoes and place them in a brown paper bag to help speed up the process. You can find more information at >>> http://www.... tomatogardeningguru. com/

And in addition to ripening vegetables or fruit in the paper bag, as Nomdeplume has stated, it is enhanced and acts faster with the addition of an apple in the bag.  You see an apple releases ethylene, a natural gas in the process of ripening, so it boosts what that which you want to ripen to give it a jump start!   For this reason, bananas will ripen (and spoil prematurely) if put too close to apples in a fruit basket. 

Some tomatoes never go red, for example the variety Green Grape is always green and is a very sweet variety.