To keep your avocados from turning brown, seal them together with a cut onion. I have a little plastic container, but you can also place them in a ziplock bag. The onion will keep the avocado green longer!
Check out these photos.
My sister has a grove of Avocados in Homestead, Florida, (just south of Miami) and she brought me some beautiful Butter Avocados and just could not resist sharing this picture. These are smaller than normal if you can believe that!