I really burst my husband's bubble last week when he proudly told me how he gave some of the 'Indigo Blue' tomatoes I've been growing away to someone we know. He said they were beautiful and "totally blue and ripe". When I told him that not a single one was even close to being ripe, and the blue color had nothing to do with ripeness, he got very defensive. "Well how in the world do you tell if it's ripe if the blue has nothing to do with it?!?!" he asked.
Only the parts of the tomato in the sun will develop the blue color, in the span of about a week. Any part that remains shaded will stay green, and ripen to red just like any other tomato. A few of my tomatoes are completely blue. For those tomatoes, the blue color will appear dull instead of shiny and the tomato will soften when ripe.
A few days after our heated debate on how to gauge ripe blue tomatoes, I was trying to keep my 15 month old son from picking the plant clean (he thinks all the tomatoes are balls and of course he wants to play with all the balls). I noticed that one of the tomatoes was in fact ripe. I spied a small area of red on an otherwise blue tomato. Finally!
When I sliced it open, it revealed it's typical tomato-red interior. I think the tomato was not quite fully ripe, but I couldn't contain my excitement to taste the famed blue tomato. It tasted just like a typical homegrown tomato should-- lots of great vine ripened flavor. Plus I think it would look amazing sliced on top of a salad or in any other fresh way to serve tomatoes. Cooking the blue tomato will destroy the blue pigment.