One of the first things most users do is to customize the look & feel of Emacs.
When you start Emacs for the first time you are most likely to see a black text against a white background. If you find these colors unsatisfactory, you can switch to a different set of colors by choosing a Custom Theme of your liking. For example, when you configure your Emacs to use the wombat theme, you get a white text on a black background.
Once you switch to a different theme, using the steps outlined below, Emacs would have generated the following customization in your .emacs.
(custom-set-variables '(custom-enabled-themes (quote (wombat))))
Custom Themes are widely used for settings the colors used by Emacs. However, they have a much broader application. For example, when you are new to Emacs, and wouldn’t bother with customizing all the bells and whistles, you can borrow a theme from your friend and use it immediately.
A program file in stock Emacs
The same program file as seen on a Emacs using wombat theme
Step 1: Launch the Custom Themes Menu
Step 2: Choose a theme, say wombat
When you choose a theme, you aren’t limited to just a single theme. You can choose as many themes as you wish. When multiple themes are active, preferences in later themes take precedence over the earlier ones. If you are still unhappy with the custom themes, you can modify them further by adding your own customizations.
Emacs Notes 