From MozillaZine Knowledge Base

You can change the background colors in Thunderbird's (or Mozilla Suite's) preview pane, folders pane, and message list pane, etc. by modifying your user.js and userChrome.css files as described below.

For the preview pane, put this in your "user.js" file:

// Previewpane Background color
user_pref("browser.display.background_color", "#F1F1F1");

For the folders pane and message-list pane, put this in your "userChrome.css" file:

/*  Folderpane & Messagepane */
treechildren {
background-color: #F1F1F1 !important; }

For other color codes, you can use this color blender.

External links

• Add alternating background colors in the message-list pane.