Try this... Click on your messages icon... Click the BB icon to bring up the menu... Select Options from the menu... Go to general options... I believe in general options you will see a option to set the message box to "theme default."
I would also try a battery pull restart if you haven't already... Take battery out of phone while phone is still on and unplugged, wait 45 seconds, put battery back in and turn phone back on.
First, thank for your reply. Then, I try as you said but nothing happen. There is only 1 option related Theme & SMS in " General Option " : SMS and Email Inboxes option . It have 3 options : Theme Controlled , Combine and Separate. I chose " Theme Controlled" . Nothing happened.