My package files are autoset to open in
S3PE, which is a wildly popular TS3 package editing program and thus that is the file icon they display. But it doesn't really matter to the game. If you have a different game/program that uses the same file extension type (such as TS4 for example) then you will likely get a different than maybe expected icon for at least some of them, meaning depending on which game you are working with at the moment.
The games themselves don't care what the icon or auto-open file settings are, they will read TS3 package files (or TS4 ones, etc.) and use them exactly the same even if they have the blank paper or some other icon showing.