Heirloom Tomatoes: WTF!

I go to Whole Foods all the time when I'm hungry, and it's so stupid because I always walk out with $200 worth of vegetables I have to work around the clock to eat before they go bad. But everything looks good and I'm helpless against the temptation of "the wild bunch" mushroom pack and $4.99/lb cherries.

So last night I walked out with a bag of heirloom tomatoes. The best description I found was on this person's flickr page: "A true heirloom tomato is a cultivar whose seeds had been nurtured, selected, and handed down from one family member to another for many generations. What allows it to maintain the heirloom name is that no genetically modified organism (GMO) can be used in its production. It conjures up an image of backyard plant grown from hard-sought seeds, of rare fruit bursting in summer's heat."

I got home and sliced one up, and I was totally unprepared for what was inside. The exterior of this plant was green fading into red, and the interior was pretty much the same except it was black. Black, as in rotten? But the black flesh wasn't crumbly or mushy like rotting fruit is; it was as firm and clean as the rest of the tomato. Humm, must just be the color, I thought, and ate a mouthful of black tomato. Wrong! It was very, very bitter. And weird. So my next thought was: is this normal?

Let me do some more investigative work and get back to you.