This Problem does often happen, when the SimPE cache got corrupted (maybe because SimPE did crash once while you were recoloring), or the FileTable was not set correct.

Here is what you can check:

1. In Extra->Preferences...: Make sure that all the listed Paths are correct. You can use the Browse... Button to validate that the Paths point to the corrrect Directories (which are the install Dirs of the Game, and the EPs, and the Folder that contains your "Downloads" Directory)
   
2. In Extra->Preferences... on the FileTable Tab: Reset the FileTable, and click Reload. Make sure that the Filetable listing does not contain any missing Lines (except of course if you did not install the EP that it refers to (EP1 is University, EP2 is Nightlife, EP3 is Open For Business...).
   
3. In Extra->Preferences... on the SimPE Settings Tab: Clear the SimPE Cache, and restart SimPE
   

This should bring back your Object in the ObjectWorkshop and Wizards of SimPE.