Tableau uses default formatting that includes default fonts, colors, shading, and alignment. Additionally, there are several levels of formatting you can customize, as shown in the following diagram:
Workbook level: The following type of formatting comes under this category:
Workbook defaults: from the menu, select Format | Workbook. The ability to set certain formatting as the default for the workbook is new to Tableau 10.
Default field formatting: Using the drop down menu on a field in the data pane, navigate to Default Properties | Date Format or Default Properties | Number Format. This sets the default format in Tableau's metadata and will be applied to any view where custom formatting has not been applied.
Story level: Navigate to a story tab and navigate to Format | Story (or Story | Format) to edit formatting for story specific elements. These include options for customizing shading, title, navigator, and description.
Dashboard level...