Try looking for existing themes for inspiration (it's what I'm doing for CH's new theme).
Here are some that may help inspire:
http://fav.me/d5mm9yd
http://fav.me/d1wdhyz
http://www.freecsstemplates.org/preview/earthling/
http://www.freecsstemplates.org/preview/earthlingtwo/
http://fav.me/d2a4rua
http://fav.me/d38wo60
http://fav.me/d2y5q0x
http://fav.me/d2tou4b
http://fav.me/d1j3xtk
Also these color themes may help as well:
http://www.colourlovers.com/palettes...uery=grassland
Then while you work on the theme, be sure to log all resources so that you can credit the creators. ;3
Hope the inspiration helps.