Fixed [Issue #6] - IE9 fallback support for linear gradients

Hey,

I believe I was able to fix the rendering in IE9. I added background color styles in the base.yaml and slate.yaml for the elements that were rendering incorrectly. IE9 does not support linear gradients so it needed a background color to fallback to. Now it seems to render correctly on my IE9, but I'm not 100%. Please review this and let me know.

If you find problems with it let me know and I'll be happy to fix and resubmit the pull request.

![graphite-fix](https://f.cloud.github.com/assets/706967/481098/fdd20a30-b849-11e2-9ad1-cef615f37b72.png)