changed sidebar content color so that it does not all change color on hover

As discussed in [this issue](https://github.com/imathis/octopress/issues/1403) - the sidebar of the default octopress theme highlights ALL contained links when you hover it.

I tracked the issue down, and it was because the sidebar contains only links - and these are displayed with your default link coloring which is only visible on hover.

This should fix it.