Took a peek (I use classic, not 2.0, and I don't have those bars). But it looks like:
Green bar is how many calories you have logged as eaten.
Yellow is how many calories you have expended through exercise.
Red is how many calories you burn during lifestyle (not exercise, just by normal daily activity).
Basically, if you burn (total) 500 more than you eat daily, you will lose a pound a week (to lose a pound, you have to burn 3500 more than you eat; 500 per day times 7 days is 3500). To lose 2 pounds a week, you need to have a calorie deficit (burned minus eaten) of 1000 calories a day. I think burned minus eaten is what you are seeing as "net calories."
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days