fix icon colors of sorin theme in other terminal themes.

By default the sorin theme colors don't render correctly in several terminal themes for example solarized dark & light.

the screenshot below shows how the sorin theme looks by default in Iterm 2 + solarized dark:
![screen shot 2014-03-30 at 15 49 31](https://cloud.githubusercontent.com/assets/1220084/2561429/4fba6bfe-b816-11e3-8a64-d2b04ae91cba.png)

as you can see, both the color of second and third arrow and the git icons don't render correctly.

the screenshot below shows the result after applying this commit:
![screen shot 2014-03-30 at 15 52 36](https://cloud.githubusercontent.com/assets/1220084/2561431/7aae4f60-b816-11e3-81e5-717f199b0663.png)

As you can see after applying this commit both the icons and arrows render correctly.