If your heirloom tomatoes are refusing to turn red, you need to consider what varieties of tomatoes you have planted. Many modern gardeners may not be familiar with every single heirloom variety there is. Some, such as the Green Zebra, will never turn red but will nonetheless be incredibly ripe and tasty while green. Check your heirloom's characteristics before becoming concerned about its lack of redness. If it should be turning red, you can coax it to do so in the same way you would with other tomatoes.
Make sure your heirloom tomato plants are getting full sun. All tomato plants need full sun, and temperatures between 50 and 85 degrees Fahrenheit to produce the chemicals that help them to ripen.
Move heirloom tomato plants that are in containers around to follow the path of the sun. If you are not home a lot, this may not be an option for you. It is a good option if you have the time.
Place picked, unripe heirloom tomatoes inside a brown paper bag. Leave them on a counter at room temperature for a few days and check to see if they have ripened and turned red.