Blue Tomatoes are a relatively new class of tomatoes. They are not only blue, but varying shades of purple as well. The color isn't the only thing different about them, they have a different taste than conventional tomatoes as well. They still have a "tomatoey" taste - but sweeter , more concentrated natural sugars and an added anti-oxidant kick from elevated levels of anthocyanin, a naturally occurring antioxidant traditionally found in blueberries and raspberries. They are extra nutritious.
They are NOT GMOs, Genetically Modified Organisms, They were developed with traditional breeding techniques.
The anti-oxidant Anthocyanin is what gives the tomatoes their blue coloring. There are a number of different varieties each with its own unique characteristics.
Indigo Rose, developed by Jim Myers of Oregon State University's was introduced in 2012. Another variety comes from tomato breeder Bradley Gates of Wild Boar Farms who now sells them at nurseries.
The pigmentation in these blue tomatoes increases when the skin is exposed to more sunlight. Only the skin is blue or Purple, the inside of the tomato is still "tomato-red".
Another recently bred variety comes from Tater Mater Seeds. Known as the 'Blue-Green Zebra' it has a green-fleshed fruit with blue and green striped skin.
There are other blue tomato varieties developed by splicing color genes from snapdragons and blueberries onto the tomatoes genes. Because of this tinkering at the genetic level, they are considered GMOs.