I was annoyed when I installed a color theme which I did not like. But there was no way to go back to the default theme because the theme made itself the default one! However, I came across the Eclipse Color Themes site. It has a good collection of decent themes. However, to try one you need to download the theme and then import and apply it. This is a painful process unless you install their cool color theme plugin. It is very easy to use and come pre-populated with the themes found in the site. You can import more and switch between the themes very easily. It is really worth giving a try.