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Microsoft SharePoint 2013. SharePoint 2013 Sites.
How to change a site theme in SharePoint 2013.
If you want to change the default blue theme of a SharePoint 2013 site, you can easily do this using a number of built in look and feel designs. Changing a theme may be very useful for your sites organization. If you have a complex sites hierarchy,the sites may blur together and look very similar to each other. Changing themes for a separate site or for a set of related sites may help to make navigation better and also improve your brand. Changing themes is a first step on the way of SharePoint branding and customization.