Hi welcome to my hobby site, my name is Mao and i use google sites as it offers an easy and quick way of implementing no fuss websites.
As a graphic designer i needed the look of my sites to compliment the google sites application. Due to the limited access to style your site the only way i could get some great graphics into this system is via the background.
These are not themes but rather background images. Its up to you to theme the site with colors that you choose to compliment the background images.
I will be supplying background themes regularly so make sure you sign up to the discussion forum to receive the latest news. I will also be lurking the forums to help out as best i can and ask questions as i don't know everything about google sites and keen to find out more.
Enjoy and peace...