Zenash is a low-saturation, light-background version of zenburn. Maybe 'zendust' would be a more descriptive name.
I dislike the highly contrasting colors of most color-themes because while they are excellent for highlighting different syntactic elements of source code files, they are also tiring when I am trying to concentrate on the semantics. For zenash, I tried to use the least contrast that I need to distinguish between syntactic elements, say, a keyword from a variable.
Also, certain elements, such as comments and parentheses, are intentionally pushed towards the background so that they are almost unnoticable unless you are looking for them.
Finally, there are many parts of emacs that I don't use, so some of the fonts might be inappropriate or plain ugly.
Original Author of zenburn.el: Daniel Brockman email@example.com
Modifier: Yavuz Arkun