As you probably know, the SSRS Report Wizard allows users to select predefined report styles. These styles are basic “skins” that apply to report foreground and background colors.
A question came in from a student as to how to modify/add styles. You can alter the existing style templates or add new ones by editing the StyleTemplates.xml file in the \Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Business Intelligence Wizards\Reports\Styles\<language> folder. You need to make this change on the client machine where SSDT is installed.
On the subject of styles, recall that starting with SQL Server 2008 R2, SSRS supports report parts to promote report reuse and reduce maintenance.