The green outline is most likely caused by sublimelint. If you click in the green area you should see something in the status area telling you why it is highlighted. Users have reported performance issues with SublimeCodeIntel before, so if you are having lockups, I would try disabling that. sublimelint may also cause issues since it is running background processes to check the syntax of the file you are working on. The easiest way to figure this out is to try disabling them one at a time.
In terms of the colors, there are two aspects to the interface in Sublime, color schemes and themes. Color schemes control the color of text in the editor pane. It sounds like you are using Space Cadet right now. Themes control the look of the editor interface. You are currently using Default. If you want a different look, you should look at the Soda theme. You can grab it from Package Control. After installing, open Preferences > Global Settings – User and add one of the following:
"theme": "Soda Light.sublime-theme"
"theme": "Soda Dark.sublime-theme"