Is there a theme or a workaround available to display e-mails in my inbox in alternating colors (e.g. odd and even lines differ in coloring)?
You can use a custom stylesheet (CSS) to do this. Just apply the styles
with colors of your choice. (The class you need to use may vary — it was
(Here are instructions for custom stylesheets in Firefox; other browsers may have other extensions which let you do this.)