I downloaded and imported an Eclipse theme and it did not look good, I believe because I also have Epic installed. Is there a Reset All? I'm afraid I will need to re-install. I have tried Restore Defaults on each node in preferences but have not been able to get all of them (like the workspace background color). Maybe there is a config file to delete?
The top answer on this post on StackOverflow describes how to change the theme in Eclipse. There are two files that you want to modify, or in your case restore to their original settings. You should be able to extract those files from the original Eclipse distribution package and replace the modified ones. Of course, back up the current files first just in case.