Green label is lower grade. They break easier, don't fit as consistently, and don't feed as well. They're also much cheaper. You get what you pay for.
Not to say what you're buying is useless... they *might* work for you, but as with most things in life, there's a phrase that almost always applies: "buy cheap, buy twice." If they work perfectly fine for you, then either you were lucky, or you have low standards and aren't a spoiled prima donna. LOL