The new Metropolis Blue theme is variant on our current Metropolis theme which we introduced in late 2012:
Metropolis: A stunning new theme inspired by modern Windows 8 UI & Office 2013 (v2012.2)
What's new about Blue?
The new Metropolis Blue theme's main difference from Metropolis is the blue instead of orange that you can see here.
We provided this theme because customers like the Metropolis theme a lot and wanted a different color.
SharePoint 2013 Blue
The blue color is the same one from SharePoint 2013. This way, you also get a theme that is similar to SharePoint 2013.
Read more: Mehul Harry's DevExpress Blog