Green is for pets over 25 pounds. Blue is for pets from 2-25 pounds. All Sales Final. Boxes may be different as they change the design. Dede loves this product as a fast way to get ahold of fleas. It's for 24 hour fix. Then you need to do other things, see this newsletter Dede has about fleas to help guide you. https://www.myfavoritegroomer.com/april-2011