When you try to create a database backup but without having selected a table, you get an error message:

You must select at least one table.

This message is displayed as a success message with green background instead of an red error message.

Fix:
Change

trigger_error($user->lang['TABLE_SELECT_ERROR'] . adm_back_link($this->u_action));   

in acp_database.php to

trigger_error($user->lang['TABLE_SELECT_ERROR'] . adm_back_link($this->u_action), E_USER_WARNING);   

Edit:
The same applies to

trigger_error($user->lang['RESTORE_FAILURE'] . adm_back_link($this->u_action));