The EmacsWiki has had its current theme for a couple of years now - Alex was open to the idea of a new default theme, so I tried making one that combined different elements of the existing alternate themes, starting from the Cali+ theme - http://i.imgur.com/NCjDpe3.png - we've been testing it out for a few weeks now.
The idea was just to make something that new users might find appealing, as veteran users can use any theme they like (though it took me a couple of years to realize you could do that!).
The logo is just a temporary placeholder - just wanted to add some color to the page. If someone has some logo design skills and wants to try making one, that would be great! Same for the title look also.