Check mark next to some apps on SD card?

[doowopper]

In my Droid X, when I go to Settings>Applications>Manage Applications>On SD Card, to the right of some of the apps is a green box with a check mark in the box. To the right of the other apps on the SD card is a grayed out box. I cannot turn the green box into a gray box and I cannot turn the gray box into a green box by tapping on the box.

What does the green box indicate and what does the grayed out box indicate? What changes the box from green to gray and gray to green?
Thanks.
Richard