The blue theme matches the other OpenEnergyMonitor web pages e.g. forum, learn, homepage etc. I think the blue theme looks much cleaner, a fresh start for 2018
The chance will effect new installations and emonPi systems where no user changes have been made to settings.php. It’s easy enough to change the theme back if you don’t want the blue theme, just set $themecolor = standard to revert back to black!
Comparison of Standard (black), Blue and Sun theme: